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I 




A TREATISE 


ON 


MASONRY CONSTRUCTION. 


s 


BY 

IRA O, BAKER, C. E., 

' \ 

PROFESSOR OF CIVIL ENGINEERING, UNIVERSITY OF ILLINOIS. 


NINTH EDITION, REVISED AND PARTIALLY REWRITTEN, 

FIRST THOUSAND. 

* i 

# * * 

> 5 ) 

v 2 . / a * 

NEW YORK: 

JOHN WILEY & SONS. 

London: CHAPMAN & HALL, Limited. 

1899. 

A ' 



V v T 





7~A byo 

.B ib 

1^1 


42696 

Copyright, 1889, 1899, 

BY 

IRA. O. BAKER. 


- ♦ 


TWO COPIES RECEIVED. 





j.i) 


ROBERT DRUMMOND, EL.ECTROTVPKR AND PRINTER, NEW YORK.. 


CcCOuD COPY, 

o S 
eto. 


4‘ 


Iff 


V 






PREFACE. 


The present volume is an outgrowth of the needs of the author’s 
own class-room. The matter is essentially that presented to his 
classes for a number of years past, a considerable part having been 
used in the form of a blue-print manuscript text-book. It is now 
published for the greater convenience of his own students, and with 
the hope that it may be useful to others. The author knows of no 
work which treats of any considerable part of the field covered by 
this volume. Nearly all of the matter is believed to be entirely new. 

The object has been to develop principles and methods and to 
give such examples as illustrate them, rather than to accumulate 
details or to describe individual structures. The underlying prin¬ 
ciples of ordinary practice are explained ; and, where needed, ways 
are pointed out whereby it may be improved. The common theo¬ 
ries are compared with the results of actual practice ; and only 
those are recommended which have been verified by experiments 
or experience, since true theory and good practice are always 
in accord. The author has had the benefit of suggestions and 
advice from practical masons and engineers, and believes that the 
information here presented is reliable, and that the examples cited 
represent good practice. The general prices are the average of a 
large number actually paid ; and the special prices are representa¬ 
tive. The structures illustrated are actual ones. The accredited 
illustrations are from well-authenticated copies of working drawings, 
and are presented without any modification whatever ; while those 
not accredited are representative of practice so common that a single 
name could not properly be attached. 

In the preparation of th£ book the endeavor has been to observe 
a logical order and a due proportion between different parts. Great 
care has been taken in classifying and arranging the matter. It 
will be helpful to the reader to notice that the volume is divided 
successively into parts, chapters, articles, sections having small-cap¬ 
ital black-face side-heads, sections having lower-case black-face side- 
heads, sections having lower-case italic side-heads, and sections hav¬ 
ing simply the serial number. In some cases the major subdivis* 




IV 


PREFACE. 


ions of the sections are indicated by small numerals. The constant, 
aim has been to present the subject clearly and concisely. 

Every precaution has been taken to present the work in a form 
for convenient practical use and ready reference. Numerous cross, 
references are given by section number ; and whenever a figure or a 
table is mentioned, the citation is accompanied by the number of 
the page on which it may be found. The table of contents shows 
the general scope of the book ; the running title assists in finding 
the different parts; and a very full index makes everything in the 
book easy of access. There are also a number of helps for the 
student, which the experienced teacher will not fail to recognize 
and appreciate. 

Although the book has been specially arranged for engineering 
and architectural students, it is hoped that the information con¬ 
cerning the strengths of the materials, the data for facilitating the 
making of estimates, the plans, the tables of dimensions, and the 
costs of actual structures, will prove useful to the man of experience. 
Considering the large amount of practical details presented and 
the great difference in the methods employed by various construc¬ 
tors, it is probable that practical men will find much to criticise. 

• The views here expressed are, however, the results of observation 
throughout the entire country, and of consultation and correspond¬ 
ence with many prominent and practical men, and represent average 
good practice. The experienced engineer may possibly also feel 
that some subjects should have been treated more fully ; but it is 
neither wise nor possible to give in a single volume minute details. 
These belong to technical journals, proceedings of societies, and 
special reports of particular work. 

No pains have been spared in verifying data and checking re¬ 
sults. The tables of cubic contents have been computed by differ¬ 
ent processes by at least two persons, and to at least one more place 
than is recorded. Should any error, either of printer or author, 
be discovered—as is very possible in a work of so much detail, 
despite the great care used,—the writer will be greatly obliged by 
prompt notification of the same. 

The author gratefully acknowledges his indebtedness to many 
engineers for advice and data, and to his former pupil and present 
co-laborer. Prof. A. N. Talbot, for many valuable suggestions. 

Champaign, III., July 9, 1889. 



PREFACE FOR NINTH EDITION. 


% 


Chapters III and IV—Cement, and Mortar and Concrete— 
have been entirely rewritten, and Chapter IIIa —Sand, Gravel, 
and Broken Stone—has been added. Many minor changes have 
been made in the remainder of the book. 

Champaign, III., June 27, 1899. 

v 







TABLE OF CONTENTS. 


PART I. THE MATERIALS. 

PAGE 


CHAPTER I. NATURAL STONE. 

Introduction...1 

Art. 1. Requisites for Good Building Stone 

Art. 2. Testing Building Stone. 

Weight . 

Hardness and Toughness . 7 

Strength. Crushing Strength. Transverse Strength. Elasticity. . 8 

Durability. Destructive Agents : mechanical, chemical. Resisting 
Agents : chemical composition, physical structure, seasoning. Meth¬ 
ods of Testing Durability : absorptive power, methods and results; 
effect of frost, methods and results; effect of atmosphere, methods 


and results. Methods of Preserving.14 

Art. 3. Classification and Description of Building Stones. . . 23 

Classification : geological, chemical, physical. Description of Trap, 
Granite, Marble, Limestone, and Sandstone. Location of Quarries. 
Weight of Stone. 

CHAPTER II. BRICK. 

Process of manufacture. Classification. Requisites for good Brick. 
Methods of Testing: absorbing power, transverse strength, crushing 


strength; results. Size. Cost.33 

CHAPTER III. LIME AND CEMENT. 

Classification.48 

Art. 1. Common Lime.49 

Methods of manufacturing, testing, and preserving. Cost. 

Art. 2. Hydraulic Lime.51 

Art. 3. Hydraulic Cement. 51 

Description : Portland, Natural, Pozzuolana. Weight. Cost. 

Art. 4. Methods of Testing Hydraulic Cement.56 


Color, Thoroughness of Burning, Activity, Soundness, Fineness, 
Strength. 


vii 


M id tO 















Yin 


TABLE OF CONTENTS. 


PAG* 

Art. 5. Specifications for Cement.6? 

Quality: German, English, French, American, Philadelphia. De¬ 


livery and Storage. 

CHAPTER IIIa. SAND, GRAVEL, AND BROKEN STONE. 

Art. 1. Sand.79 a 

Requisites for Good Sand : Durability, Sharpness, Cleanness, Fine¬ 
ness, Voids. Stone Screenings. Cost. Weight. 

Art. 2. Gravel and Broken Stone.79 k 

Gravel. Broken Stone. Voids. Weight. Cost. 


PART II. PREPARING AND USING THE MATERIALS. 

CHAPTER IV. MORTAR, CONCRETE, AND ARTIFICIAL STONE. 

Art. 1 Mortar.81 

Lime Mortar. Cement Mortar : proportions and preparation. 
Data for Estimates. Strength: tensile, compressive, adhesive. Cost. 
Effect of Re-tempering. Lime with Cement. Mortar Impervious to 


Water. Effect of Freezing. 

Art. 2. Concrete.10G 

Mortar. Aggregate. Proportions : theory, determination, data 
for estimates Mixing. Laying. Strength. Cost. 

Art. 3. Artificial Stone.* . 1136 

Portland. McMurtrie. Frear. Ransome. Sorel. 

CHAPTER V. QUARRYING. 


Methods of Quarrying : by hand tools ; by explosives,—the drills, 


the explosives ; by channeling and wedging. 116 

CHAPTER VI. STONE CUTTING. 

Art. 1. Tools.125 

Eighteen hand tools illustrated and described. Machine tools de¬ 
scribed. 

Art. 2. Methods of Forming the Surfaces.129 

Four methods illustrated and described. 

Art. 3. Methods of Finishing the Surfaces.131 

Eight methods illustrated and described. 


CHAPTER VII. STONE MASONRY. 

Definitions : parts of the wall, kinds of masonry. Ashlar Masonry: 
dressing, bond, backing, pointing, mortar required, when employed, 
specifications. Squared-stone Masonry : description, mortar required, 
specifications. Rubble Masonry: description, mortar required, when 
employed, specifications. Slope-wall Masonry. Stone Paving. Rip- 















TABLE OF CONTENTS. 


IX 


PAGE 

rap. Strength of Stone Masonry : examples, safe pressure. Meas¬ 
urement of masonry. Cost: quarrying, dressing, price of stone; 
examples—U. S. public buildings, railroads, tunnels, bridge piers, 
arch culverts ; summary. 135 

CHAPTER VIII. BRICK MASONRY. 

Mortar. Bond. Compressive Strength: results of experiments, 
safe pressure. Transverse Strength : strain on lintel. Measurement 
of Brick-work. Data for Estimates: brick, labor, mortar required. 
Cost. Specifications : for buildings, sewers, arches. Brick vs. Stone 
Masonry. Brick Masonry Impervious to Water. Efflorescence. . . 161 


PART III. FOUNDATIONS. 

CHAPTER IX. INTRODUCTORY. 

Definitions, and Plan of Proposed Discussion. .... 183 
CHAPTER X. ORDINARY FOUNDATIONS. 


Outline of Contents .186 

/Abt. L The Soil .186 


Examination of the Site. Bearing power of Soils : rock, clay, sand, 
semi-liquid soils ; summary. Methods of Improving Bearing Power: 
increasing depth, drainage, springs, consolidating the soil, sand piles, 
layers of sand. 

Art. 2. Designing the Footings...199 

Load to be Supported. Area Required. Center of Pressure and 
Center of Base. Independent Piers. Effect of Wind. Offsets for 
Masonry Footings. Timber Footings. Steel-rail Footings. Inverted 
Arches. 

Art. 3. Preparing the Bed.213 

On Rock. On Firm Earth. In Wet Ground : coffer-dam, con¬ 
crete, grillage. 

CHAPTER XI. PILE FOUNDATIONS. 

Definitions.216 

Art. 1. Descriptions, and Methods of Driving Piles.216 

Description : iron piles ; screw piles ; disk piles ; sheet piles ; bear¬ 
ing piles,—specifications, caps and shoes, spliciug. Pile Driving Ma¬ 
chines: drop-hammer,—friction clutch, nipper; steam-hammer, drop- 
hammer vs. steam-hammer ; gunpowder pile-drivers ; driving with 
dynamite ; driving with water jet; jet vs. hammer. Cost of Piles. 

Cost of Pile Driving: railroad construction, bridge construction, 
•bridge repairs, foundations, harbor and river work. 












X 


TABLE OE CONTENTS. 


PAGm 

Art. 2. Bearing Power of Piles.233 

Methods of Determining Supporting Power. Rational Formula. 
Comparison of Empirical Formulas: Beaufoy’s, Nystrom’s, Mason’s, 
Sander’s, McAlpine’s, Trautwine’s, the Author’s. Supporting Power 
Determined by Experiment: examples, factor of safety; supporting 
power of screw and disk piles. 

Art. 3. Arrangement of tile Foundation.250 

Position of Piles. Sawing-off. Finishing Foundation: piles and 
grillage, piles and concrete, lateral yielding. Cushing’s Pile Founda¬ 
tion. 

CPIAPTER XII. FOUNDATIONS UNDER WATER. 

Difficulties to be Overcome. Outline of Contents. . . 257 

Art. 1. The Coffer-Dam Process.258 

Construction of the Dam. Leakage, pumps. Preparing the 
Foundation 

Art. 2. The Crib and Open Caisson Process.26G 

Definitions. Principle. Construction of the Caisson. Construc¬ 
tion of the Crib. Excavating tne Site. 

Art. 3. Dredging through Wells.271 

Principle. Excavator. Noted Examples: Poughkeepsie, Atcha- 
falaya, and Hawkesbury bridges; brick cylinders. Frictional Resist¬ 
ance. Cost. 

Art. 4. Pneumatic Process.278 

Vacuum Process. Plenum Process. History. Pneumatic Piles, 
bearing power. Pneumatic Caissons : the caisson, the crib, the coffer¬ 
dam, machinery, air-lock. Excavators: sand lift, mud-pump, water 
column, blasting. Rate of Sinking. Guiding the Caisson. Noted 
Examples : Havre de Grace, Blair, St. Louis, Brooklyn, Forth Bridges. 
Physiological Effects of Compressed Air. Examples of Cost: at 


Havre de Grace, Blair, and Brooklyn, and in Europe. 

Art. 5. The Freezing Process.307 

Principle. History. Details of Process. Examples. Advantages. 

Cost. 

Art. 6. Comparison of Methods.30<> 


PART IV. MASONRY STRUCTURES. 

CPIAPTER XIII. MASONRY DAMS. 


Classification of Dams.311 

Art. 1. Stability of Gravity Dams.312 


Principles. Stability against Sliding: destroying forces, resisting 
forces, co-efficient of friction, condition of equilibrium, factor of 
safety. Stability against Overturning : by moments,—overturning mo- 















TABLE OF CONTENTS. 


XI 


ment, resisting moment, condition for equilibrium, factor of safety ; 
by resolution of forces. Stability against Crushing : method of find¬ 
ing maximum pressure, tension on masonry, limiting pressure. 

Art. 2. Outlines of the Design. 

Width on Top. The Profile: theory, examples. The Plan : 
straight crest vs. straight toe ; gravity vs. arch dams ; curved gravity 
dams. Quality of Masonry. Bibliography. 

Art. 3. Rock-Fill Dams. 

Wood. Earth. Rock-fill and masonry dams compared. 

* 

CHAPTER XIV. RETAINING WALLS. 

Definitions. Methods of Failure. Difficulties. ....... 

Art. 1. Theoretical Formulas. 

The Three Assumptions. Theories: Coulomb’s, Weyrauch’s, 
Rankine’s. 

Art. 2. Empirical Rules. 

English Rules. American Rules. Details of Construction : quality 
of masonry, drainage, land ties, relieving arches. 

CHAPTER XV. BRIDGE ABUTMENTS. 

Discussion of General Forms. Quality of Masonry. Foundation. 
Wing Abutment,—design, and table of contents of various sizes. 
U- Abutment,—design and table of contents of various sizes. T-Abut- 
ment,—design and table of contents of various sizes. 

CHAPTER XYI. BRIDGE PIERS. 

Selection of Site and Arrangement of Spans. . . . 

Art. 1. Theory of Stability.. . 

Methods of Failure. Stability against Sliding: effect of wind, cur¬ 
rent, ice ; resisting forces. Stability against Overturning: by mo¬ 
ments ; by resolution of forces. Stability against Crushing. Example 
of method of computing stability. 

Art. 2. Details of Construction. 

Dimensions : on top, at bottom. Batter. Cross Section. Specifica¬ 
tions. Examples : Cairo, Grand Forks, Blair, Henderson, St. Croix 
River ; iron tubular ; wooden barrel. Tables of Contents of different 
styles and sizes of bridge piers. Specifications. 

CHAPTER XVII. CULVERTS. 

Art. 1. Water Way Required. 

The Factors. The Formulas : Meyer’s, Talbot’s. Practical method 
of finding area of water way. 

Art. 2. Box and Pipe Culverts. 

Stone Box Culvert : foundation, end walls, cover, specifications. 


PAGE 

326 

334 

338 

340 

349 

353 

366 

367 
• 

377 

391 

396 














Xll 


TABLE OF CONTENTS. 


PAGE 


Examples: Standard, West Shore, Canadian. Table of Contents and 

cost of the various styles and sizes.396 

Vitrified ripe Culverts: Construction. Example Table of Con¬ 
tents.407 

Iron Pipe Culverts : Construction. Size and Weight of Pipe. Ex¬ 
amples : A., T. & S. F., and C., B. & Q. standards. Table of Quan¬ 
tity of Materials Required.412 

Timber Culvert: C., M. & St. P. standard box culverts. C., B. & 

Q. standard barrel culvert.417 

Art. 3. Arch Culvert .419 

General Form : splay of wing walls, joining wings and body, seg¬ 
mental vs. semi-circular. Examples : diagrams illustrating details, and 
also tables giving dimensions, and contents, and cost, of all sizes of 
each of the standard forms of the Illinois Central. C., K. & N., A., T. 

& S.-F. (both semi-circular and segmental), and a standard form. 
Specifications. 

• 

CHAPTER XVIII. MASONRY ARCHES. 

Definitions: parts and kinds of arches; line of resistance.440 

Art. 1. Theory of the Masonry Arch .444 

External Forces. Methods of Failure. Criteria of Safety : sliding, 
rotation, crushing,—unit pressure, open joints. Location of Line of 
Resistance : hypothesis of least pressure ; hypothesis of least crown 
thrust, joint of rupture; Winkler’s hypothesis; Navier’s principle. 
Rational Theory of the Arch: symmetrical load,—two methods; 
unsymmetrical load ; criterion for line of resistance. Scheflier’s 
Theory: two examples ; erroneous application ; reliability of. llan- 
kine’s Theory : curvature of linear arch, method of testing stability, 
reliability. Other Theories. Theory of the Elastic Arch. Stability 
of Abutments and Piers. 

Art. 2. Rules Derived from Practice.494 

Empirical Formulas: thickness of the arch at the crown,—Ameri* 
can, French, English practice ; thickness at the springing,—American, 
French, English practice ; dimensions of abutments. Dimensions of 
Actual Arches and Abutments. Illustrations of Arches. Minor De¬ 
tails : backing, spandrel filling, drainage. Brick Arches ; bond ; ex¬ 
amples,—tunnel, Philadelphia sewers, Washington sewers. Specifica¬ 
tions : stone arches, brick arches. 

Art. 3. Arch Centers.515 

Load to be supported, method of computing. Outline forms of 
Centers : solid rib, built rib, braced wooden rib, trussed frame. Ex¬ 
amples: centers for Vosburg tunnel, stone bridges, and Cabin John 
Arch. Striking Centers: method, time. 












TABLE OF CONTENTS. xiii 


APPENDIX I. SPECIFICATIONS FOP MASONRY. 

pa<;e 

General Railroad Masonry.’ . . . . 529 

Masonry of Railroad Buildings.534 

Architectural Masonry.539 


APPENDIX II. SUPPLEMENTARY NOTES. 

Labor Required in Quarrying.544 

Cost of Cutting Granite., . 545 

Cost of Laying Cut Stone.545 

Cost of Breaking Stone for Concrete.. . 546 

Cost of Imbedding Large Stones in Concrete.. . 547 

Crushing Strength of Sewer Pipe.. . 547 

Holding Power of Drift-bolts. ..547 
















MASONRY CONSTRUCTION. • 


INTRODUCTION. 

Under this general head will be discussed the subjects relating 
to the use of stone and brick as employed by the engineer or archi¬ 
tect in the construction of buildings, retaining walls, bridge piers, 
culverts, arches, etc., including the foundations for the same. 
For convenience, the subject will be divided as follows : 

Fart I. Description and Characteristics of the Materials. 

Part II. Methods of Preparing and Using the Materials. 

Part III. Foundations. 

Part IV. Masonry Structures. 



r * The first cost of masonry should be its only cost. Though superstrucnm* 
decay and drift away, though embankments should crumble and wash out, 
masonry should stand as one great mass of solid rock, firm and enduring/' 

- ~A?ionymou8. 


PART I 


THE MATERIALS. 


CHAPTER I. 

NATURAL STONE. 

Art. 1. Requisites for Good Building Stone. 

1. The qualities which are most important in stone used for 
construction are cheapness, durability, strength, and beauty. 

2. Cheapness. The primary factor which determines the value 
of a stone for structural purposes is its cheapness. The items which 
contribute to the cheapness of a stone are abundance, proximity of 
quarries to place of use, facility of transportation, and the ease with 
which it is quarried and worked. 

The wide distribution and the great variety of good building 
stone in this country are such that suitable stone should everywhere 
be cheap. That such is not the case is probably due either to a 
lack of the development of home resources or to a lack of confidence 
in. home products. The several State and Government geological 
surveys have done much to increase our knowledge of the building 
stones of this country. 

The lack of confidence in home resources has very frequently 
caused stones of demonstrated good quality to be carried far and 
wide, and frequently to be laid down upon the outcropping ledges 
of material in every way their equal. The first stone house erected 
in San Francisco, for example, was built of stone brought from 
China ; and at the present day the granites mostly employed there 
are brought from New England or from Scotland. Yet there are 
no stones in our country more to be recommended than the Califor¬ 
nia granites. Some of the prominent public and private buildings 
in Cincinnati are constructed of stone that was carried by water and 

’ 3 



4 


NATURAL STONE. 


[CHAP. I. 


railway a distance of about 1500 miles. Within 150 miles of Cin¬ 
cinnati, in the sub-carboniferous limestohe district of Kentucky, 
there are very extensive deposits of dolomitic limestone that afford 
a beautiful building stone, which can be quarried at no more ex¬ 
pense than that of the granite of Maine. Moreover, this dolomite 
is easily carved, and requires not more than one third the labor to 
give it a surface that is needed by granite. Experience has shown 
that the endurance of this stone under the influence of weather is 
very great; yet because it has lacked authoritative indorsement 
there has been little market for it, and lack of confidence in it has 
led to the transportation half-way across the continent of a stone 
little, if any, superior to it. 

Development of local resources follows in the wake of good in¬ 
formation concerning them, for the lack of confidence in home prod¬ 
ucts can not be attributed to prejudice. 

The facility with which a stone may be quarried and worked is 
an element affecting cheapness. To be cheaply worked, a stone 
must not only be as soft as durability will allow, but it should have 
no flaws, knots, or hard crystals. 

3. Durability. Next in importance after cheapness is dura¬ 
bility. Rock is supposed to be the type of all that is unchangeable 
and lasting; but the truth is that, unless a stone is suited to the 
conditions in which it is placed, there are few substances more liable 
to decay and utter failure. The durability of stone is a subject 
upon which there is very little reliable knowledge. The question 
of endurance under the action of weather and other forces can not 
be readily determined. The external aspect of the stone may fail 
to give any clue to it; nor can all the tests we yet know determine 
to a certainty, in the laboratory, just how a given rock will with¬ 
stand the effect of our variable climate and the gases of our cities. 
If our land were what is known as a rainless country, and if the 
temperature were uniform throughout the year, the selection of a( 
durable building stone would be much simplified. The cities of ! 
northern Europe are full of failures in the stones of important 
structures. The most costly building erected in modern times, per¬ 
haps the most costly edifice reared since the Great Pyramid,—the 
Parliament House in London,—was built of a stone taken on the 
recommendation of a committee representing the best scientific and 
technical skill of Great Britain. The stone selected was submitted 




TESTS OF BUILDING STONES. 


O 


ART. 2.J 


to various tests, but the corroding influence of a London atmosphere 
was overlooked. The great structure was built, and now it seems 
questionable whether it can be made to endure as long as a timber 
building would stand, so great is the effect of the gases of the 
atmosphere upon the stone. This is only one of the numerous in¬ 
stances that might be cited in which a neglect to consider the 
climatic conditions of a particular locality in selecting a building 
material has proved disastrous. 

“ The great difference which may exist in the durability of stones 
of the same kind, presenting little difference in appearance, is 
strikingly exemplified at Oxford, England, where Christ Church 
Cathedral, built in the twelfth or thirteenth century of oolite from 
a quarry about fifteen miles away, is in good preservation, while 
many colleges only two or three centuries old, built also of oolite 
from a quarry in the neighborhood of Oxford, are rapidly crumbling 
to pieces.”* 

4. Strength. The strength of stone is in some instances a 
cardinal quality, as when it is to form piers or columns to support 
great weights, or capstones that span considerable intervals. It is 
also an indispensable attribute of stone that is to be exposed to 
mechanical violence or unusual wear, as in steps, lintels, door-jambs, 
e + c. 

5. BEAUTY. This element is of more importance to the archi¬ 
tect than to the engineer ; and yet the latter can not afford to 
neglect entirely the element of beauty in the design of his most 
utilitarian structures. The stone should have a durable and pleas¬ 
ing color. 

Art. 2. Tests of the Quality of Building Stones. 

6 . As a general rule, the densest, hardest, and most uniform 
stone will most nearly meet the preceding requisites for a good 
building stone. The fitness of stone for structural purposes can ba 
determined approximately by examining a fresh fracture. It should 
be bright, clean, and sharp, without loose grains, and free from any 
dull, earthy appearance. The stone should contain no “ drys,”?.e., 
seams containing material not thoroughly cemented together, nor 
“ crow-foots,” i.e. f veins containing dark-colored, uncemented 
material. 


* Rankine’s Civil Engineering, p. 362. 





6 


NATURAL STONE. 


[chap. r. 


The more formal tests employed to determine the qualities of a 
building stone are: (1) weight or density, (2) hardness and tough¬ 
ness, (3) strength, (4) durability. 


1. Weight of Stone. 


7. Weight or density is an important property, since upon it 
depends to a large extent the strength and durability of the stone. 

If it is desired to find the exact weight per cubic foot of a given 
stone, it is generally easier to find its specific gravity first, and then 
multiply by 62.4,—weight, in pounds, of a cubic foot of water. 
This method obviates, on the one hand, the expense of dressing a 
sample to regular dimensions, or, on the other, hand, the in¬ 
accuracy of measuring a rough, irregular piece. Notice, however, 
that this method determines the weight of a cubic foot of the solid 
stone, which will be more than the weight of a cubic foot of the 
material as used for structural purposes. In finding the specific 
gravity there is some difficulty in getting the correct displacement 
of porous stones,—and all stones are more or less porous. There 
are various methods of overcoming this difficulty, which give 
slightly different results. The following method, recommended by 
General Gillmore, is most frequently used: 

All loose grains and sharp corners having been removed from 
the sample and its weight taken, it is immersed in water and 
weighed there after all bubbling has ceased. It is then taken out 
of the water, and, after being compressed lightly in bibulous paper 
to absorb the water on its surface, is weighed again. The specific 
gravity is found by dividing the weight of the dry stone by the 
difference between the weight of the saturated stone in air and in 
water. Or expressing this in a formula, 


Specific gravity = 



in which W a represents the weight of dry stone in air, W a the 
weight of saturated stone in air, W t the weight of stone immersed 
in water. 

The following table contains the weight of the stones most fre¬ 
quently met with. 




ART. 2 .] 


TESTS OF BUILDING STONES. 


7 


TABLE 1. 

Weight of Building Stones. 


Kind of Stone. 



Min. 

Max. 

Mean. 

Granites. 

161 

178 

167 

Limestones. 

146 

174 

158 

Marbles. 

157 

180 

170 

Sandstones. 

127 

151 

189 

174 

Slates. 

160 

175 



Pounds per Cubic Foot. 


2. Hardness and Toughness. 

8. The apparent hardness of a stone depends upon (1) the 
hardness of its component minerals and (2) their state of aggrega¬ 
tion. The hardness of the component minerals is determined by 
the resistance they offer to being scratched; and varies from that 
of talc which can easily be scratched with the thumb-nail, to that 
of quartz which scratches glass. But however hard the mineral 
constituents of a stone are, the apparent hardness of the stone itself 
depends upon the state of aggregation of the particles. Many 
rocks composed of hard materials work readily, because their grains 
are loosely coherent; while others composed of softer materials are 
quite tough and difficult to work, owing to the tenacity with which 
the particles adhere to each other. Obviously a stone in which the 
grains adhere closely and Btrongly one to another will be stronger 
and more durable than one which is loose textured and friable. 

The toughness of a stone depends upon the force with which the 
particles of the component minerals are held together. 

Both hardness and toughness should exist in a stone used for 
stoops, pavements, road-metal, the facing of piers, etc. No experi¬ 
ments have been made in this country to test the resisting power of 
stone when exposed to the different kinds of service. A table of the 
resistance of stones to abrasion is often quoted,* but as it contains 
only foreign stones, which are described by local names, it is not of 
much value. 


* For example, Mahan’s Civil Engineering, p. 13. 




















8 


NATURAL STONE. 


[CHAP. I.. 


3. Strength. 

Under this head will be included (1) crushing or compressive 
strength, (2) transverse strength, (3) elasticity. Usually, when 
simply the strength is referred to, the crushing strength is intended. 

9. Crushing Strength. The crushing strength of a stone is 
tested by applying measured force to cubes until they are crushed. 
The results for the crashing strength vary greatly with the details 
of the experiments. Several points, which should not be neglected 
either in planning a series of experiments or in using the results 
obtained by experiment, will be taken up separately, although they 
are not entirely independent. 

10. Form of Test Specimen. Experiments show that all brittle 
materials when subjected to a compressive load fail by shearing on 
certain definite angles. For brick or stone, the plane of rupture 
makes an angle of about 60° with the direction of the compressing 
force. For this reason, the theoretically best form of test specimen 
would be a prism having a height of about one and a half times the 
least lateral dimension. The result is not materially different if 
the height is three or four times the least lateral dimension. But 
if the test specimen is broader than high, the material is not free 
to fail along the above plane of rupture, and consequently the 
strength per unit of bed-area is greater than when the height is 
greater than the breadth. 

However, notwithstanding the fact that theoretically the test 
specimen should be higher than broad, it is quite the universal 
custom to determine the crushing strength of stone by testing 
cubes. 

11. Size of the Cube. Although the cube is the form of test 
specimen generally adopted, there is not equal unanimity as to the 
size of the cube; but it is conclusively proven that the strength per 
square inch of bed-area is independent of the size of the cube, and 
therefore the size of the test specimen is immaterial. 

General Gillinore, in 1875, made two sets of experiments which 
seems to prove that the relation between the crushing strength and 
the size of the cube can be expressed by the formula 

y = a Vx, 

in which y is the total crushing pressure in pounds per square inch 




ART. 2 .] 


STRENGTH OF BUILDING STONES. 


9 


of bed-area, a is the crushing pressure of a 1-inch cube of the same 
material, and x is the length in inches of an edge of the cube under 
trial. For two samples of Berea (Ohio) sandstone, a was 7000 and 
9500 lbs., respectively.* 

Kesults by other observers with better machines, particularly by 
General Gillmore \ with the large and accurate testing-machine at 
Watertown (Mass.) Arsenal, J uniformly show this supposed law to 
be without any foundation. Unfortunately the above relation 
between strength and bed-area is frequently quoted, and has found 
a wide acceptance among engineers and architects. 

Two inches is the most common size of the cube for compression 
tests. 

12. Cushions. Homogeneous stones in small cubes appear in 
all cases to break as shown in Fig. 1. The 
forms of the fragments a and b are, approxi¬ 
mately, either conical or pyramidal. The 
more or less disk-shaped pieces c and d are 
detached from the sides of the cube with a 
kind of explosion. In the angles e and /, the 
stone is generally found crushed and ground 
into powder. This general form of breakage 
occurs also in non-homogeneous stones when 
crushed on their beds, but in this case the modification which the 
grain of the stone produces must be taken into account. 

The nature of the material in contact with the stone while 
under pressure is a matter of great moment. If the materials which 
press upon the top and bottom of the specimen are soft and yielding 
and press out sidewise, they introduce horizontal forces which 
materially diminish the apparent crushing strength of the stone. 
If the pressing surfaces are hard and unyielding, the resistance of 
these surfaces adds considerable to the apparent strength. 



* Report on Strength of Building Stone, Appendix, Report of Chief of Engineers 
of U. S. A. for 1875. 

f Notes on the Compressive Resistance of Freestone, Brick Piers, Hydraulic 
Cements, Mortars, and Concrete, Q. A. Gillmore. John Wiley & Sons, New York, 
1888. 

X Report on the “Tests of Metals,” etc., for the year ending June 30, 1884, pp. 
126, 166, 167, 197, 212, 213, 215; the same being Sen. Ex. Doc. No. 35, 49th Cong., 
1st Session. For a discussion of these data by the author, see Engineering News x 
vol. xix. pp. 511-512. 





10 


NATURAL STONE. 


[CHAP. I. 


Formerly steel, wood, lead, and leather were much used as 
pressing surfaces. Under certain limitations, the relative crushing 
strengths of stones with these different pressing surfaces are 100, 
89, 65, and 62 respectively.* 

Tests of the strength of blocks of stone are useful only in com¬ 
paring different stones, and give no idea of the strength of struct¬ 
ures built of such stone (see § 246) or of the crushing strength of 
stone in large masses in its native bed (see § 273). 

Then, since it is not possible to have the stone under the same 
conditions while being tested that it is in the actual structure, it is 
best to test the stone under conditions that can be accurately 
described and readily duplicated. Therefore it is rapidly coming to 
be the custom to test] the stone between metal pressing surfaces. 
Under these conditions the strength of the specimen will vary greatly 
with the degree of smoothness of its bed-surfaces. Hence, to obtain 
definite and precise results, these surfaces should be rubbed or 
ground perfectly smooth; but as this is tedious and expensive, it is 
quite common to reduce the bed-surfaces to planes by plastering 
them with a thin coat of plaster of Paris. With the stronger 
stones, specimens with plastered bed will show less strength than 
those having rubbed beds, and this difference will vary also with 
the length of time the plaster is allowed to harden. With a 
stone having a strength of 5,000 to 6,000 pounds per square inch, 
allowing the plaster to attain its maximum strength, this differ¬ 
ence varied from 5 to 20 per cent., the mean for ten trials being 
almost 10 per cent, of the strength of the specimen with rubbed 
beds. 

13. Dressing the Cube. It is well known that even large 
stones can be broken by striking a number of comparatively light 
blows along any particular line; in which case the force of the blows 
gradually weakens the cohesion of the particles. This principle finds 
application in the preparation of test specimens of stone. If the 
specimen is dressed by hand, the concussion of the tool greatly 
affects its internal conditions, particularly with test specimens of 
small dimensions. With 2-incli cubes, the tool-dressed specimen 
usually shows only about 60 per cent, of the strength of the sawed. 


* Report on Building Stones, in Report of Chief of Engineers, U. S. A., 1875, App. 
II.; also bound separately, page 29. 






ART. 2 .] 


STRENGTH OF BUILDING STONES. 


11 


sample. The sawed sample most nearly represents the conditions 
of actual practice. 

Unfortunately, experimenters seldom state whether the specimens 
were tool-dressed or sawed. The disintegrating effect of the tool 
in d ressing is greater with small than with large specimens. This may 
account in part for the difference in strength of different sizes of 
test specimens. All stones are strongest when laid on their bed, i.e ., 
in their natural position; and with sedimentary rocks there is a 
very great difference in the two positions. Hence, in preparing the 
specimen the natural bed should be marked, and the position in 
which it is tested should be noted. Tests of the strength of blocks 
of stone are useful only in comparing different stones, and give no 
idea of the strength of structures built of such stone (see § 246) or 
of the crushing strength of stone in large masses in its natural bed 
(see § 273). 

14. Data on Crushing Strength. The strength of the principal 
classes of building stone in use in the United States is about as 
follows : 


TABLE 2. 

Crushing Strength of Cubes of Stone. 


Kinds of Stone. 

Ultimate Crushing Strength. 

Pounds per Square Inch. 

Tons per Square Foot. 

Min. 

Max. 

Min. 

Max. 

Trap Rocks of N. J. 

20,000 

24,000 

1,440 

1,730 

Granite. 

12,000 

21,000 

860 

1,510 

Marble. 

8,000 

20,000 

580 

1,440 

Limestone. 

7,000 

20,000 

500 

1,440 

Sandstone. 

5,000 

15,000 

360 

1,080 


15. Crushing Strength of Slabs. Only a few experiments have 
been made to determine the crushing strength of slabs of stone. 
The strength per square inch of bed-surface was considerably 
greater than that for cubes; but a study of the results of all of the 
reliable experiments * fails to discover any simple relation between 

* See Report on “Tests of Metals, etc.,” for 1884.—Sen. Ex. Doc. No. 35, 49th 
Cong., 1st Session,—pp. 126 and 212. 

























12 


NATURAL STONE. 


[chap. r. 


the crushing strength of cubes and slabs. It is probable that the 
effect of the pressing surface is so great as to completely mask the 
variation due to height of specimen. More experiments on this 
subject are very much needed. 

16. Transverse Strength. When stones are used for lintels, 

etc., their transverse strength becomes important. The ability of a 
.stone to resist as a beam depends upon its tensile strength, since 
that is always much less than its compressive strength. A knowl¬ 
edge of the relative tensile and compressive strength of stones is 
valuable in interpreting the effect of different pressing surfaces in 
compressive tests, and also in determining the thickness required 
for lintels, sidewalks, cover-stones for box culverts, thickness of 
footing courses, etc. 

Owing to the small cross section of the specimen employed in 
determining the transverse strength of stones,—usually a bar 1 inch 
square,—the manner of dressing the sample affects the apparent 
transverse strength to a greater degree than the compressive strength 
(see § 13); and it is even more unfortunate, since the strength of 
the stone as used in actual practice is nearly proportional to the 
strength of sawed samples. 

The following formulas are useful in computing the breaking 
load of a slab of stone. Let W represent the concentrated center 
load plus half of the weight of the beam itself, in pounds; and let 
b, cl, and l represent the breadth, depth, and length, in inches, 
respectively. Let R = the modulus of rupture, in lbs. per sq. in.; 
let C = the weight, in pounds, required to break a bar 1 inch 
square and 1 foot long between bearings; and let L = the length 
of the beam in feet. Then 


W = 


2 b cl 

3 r 


R = 


b cV 
L 


a 


The equivalent uniformly distributed weight is equal to twice the 
concentrated center load. 

Table 3 on the following page gives the values of R, the mod¬ 
ulus of rupture, and of C, the co-efficient of transverse strength, 
required in the above formulas. 

Example. To illustrate the method of using the above formulas, 
assume that it is desired to know the breaking load for a limestone 
slab 3 inches thick, 4 feet wide, and 6 feet long. Then b = 48; 






ART. 2 .] 


STRENGTH OF BUILDING STONES. 


15 


TABLE 3. 

Transverse Strength of Stone, Brick, and Mortar. 


Material. 

Modulus of Rupture. 

CO EFFICIENT OF TRANS¬ 
VERSE Strength. 

Max. 

Min. 

Aver. 

Max. 

Min. 

Aver. 

Blue-stone flagging. 

4,511 

360 ' 

2,700 

251 

20 

150 

Granite. 

2,700 

900 

1,800 

150 

50 

100 

Limestone. 

2,500 

140 

1,500 

140 

8 

83 

“ oolitic, from Ind., sawed. 

2,590 

2,190 

2,338 

144 

122 

130 

Marble.. . .. 

2,880 

144 

2,160 

160 

8 

120 

Sandstone. 

2,340 

576 

1,260 

130 

32 

70 

Slate. 

9,000 

1,800 

5,400 

500 

100 

300 

Brick (§ 59). 

1,796 

269 

800 

100 

15 

45 

Concrete—see § 156. 

% 






Mortar, neat Portland, 1 year old.. 



1,158* 



64* 

Mortar, 1 part Portland cement, 1 







part sand, 1 year old. 



945* 



52* 

Mortar, 1 part Portland cement, 2 







parts sand, 1 year old. 



682* 



38* 

Mortar, neat Rosendale, 1 year old. 

715 

415 

600 

39 

23 

33 

Mortar, 1 part Rosendale cement, 







1 part sand, 1 year old... .^. 

690 

348 

526 

38 

19 

29 

Mortar, 1 part Rosendale cement, 







2 parts sand, 1 year old. 

479 

338 

405 

26 

18 

22 


d = 3; l = 72; R =z 1500 lbs.,—the “average” value from the 
table ; —and C = 83. Substituting these values, we have 


W = ‘~~ r -R = 

o l 


2 X 48 X 9 
3 X 72 


1500 = 6000 pounds; 


or, using the other form, 

W = bjTp _ 48X 9 g3 _ 597g ndg) 

L 6 

which agrees with the preceding except for omitted decimals. 
Hence the breaking load for average quality of limestone is 6000 
pounds concentrated along a line half-way between the ends; tlio 
uniformly distributed load is twice this, or 12,000 pounds. The 


* Only one experiment. 


















































14 


NATURAL STONE. 


[CHAP. I. 


question of what margin should be allowed for safety is one that can 
not be determined in the abstract; it depends upon the accuracy 
with which the maximum load is estimated, upon the manner the 
load is applied—whether with shock or not,—upon the care w r ith 
which the stone was selected, etc. This subject will be discussed 
further in connection with the use of the data of the above table in 
subsequent parts of this volume. 

17. Elasticity. But very few experiments have been made to 
determine the co-efficient of elasticity, the elastic limit, and the 
“set” of stone. Data on these points would be valuable in deter¬ 
mining the effect of combining masonry and metal, of joining 
different kinds of masonry, or of joining new masonry to old ; in 
calculating the effect of loading a masonry arch ; in projDortioning 
abutments and piers of railroad bridges subject to shock, etc. 
The following is all the data that can be found: 

TABLE 4. 

Co-efficient of Elasticity of Stone, Brick, and Mortar. 


Material. 

Haverstraw Freestone *. 

Portland Stone (oolite limestone)!. 

Marblef. 

Portland Granite!. 

Slatef. . 

Grafton Limestone!. 

Richmond Granite! . 

Brick, medium—mean of 16 experiments*. 

Louisville Cement Mortar, 4 months old : ! 

Neat cement... 

1 part cement, 1 part sand. 

1 part cement, 2 parts sand. 

Ulster Co. (N. Y.) Cement Mortar, 22 months 

old:* 

2 parts cement, 3 parts sand. 

1 part cement, 3 parts sand. . 

Portland Cement Mortar, 22 months old*. 


Pounds per Square Inch. 


950,000 

1,530,000 

2,500,000 

5,500,000 

7,000,000 

8,000,000 

13,000,000 

3,500,000 

800,000 

600,000 

1,300,000 


640,000 

535.000 

1,525,000 


* U. 8. testing-machine, Watertown, Mass. t Tredgold, as quoted by Stoney, 

X History of St. Louis Bridge, pp. 324-28. 
























ART. 2 .] 


STRENGTH OF BUILDING STONES. 


15 


18. Bibliographical. A large number of tests have been 
applied to the building stones of the United States. For the 
results and details of some of the more important of these tests 
see: Report on Strength of Building Stone, Gen. Q. A. Gillmore, 
Appen. II, Report of Chief of Engineers, U. S. A., for 1875; 
Tenth Census of the U. S., Vol. X, Report on the Quarry 
Industry, pp. 330-35; the several annual reports of tests made 
with the U. S. Government testing machine at the Watertown 
(Mass.) Arsenal, published by the U. S. War Department under 
the title Report on Tests of Metals and Other Materials; 
Transactions of the American Society of Civil Engineers, Yol. II, 
pp. 145-51 and pp. 187-92; Journal of the Association of En¬ 
gineering Societies, Yol. Y, pp. 176-79, Yol. IX, pp. 33-43; 
Engineering News, Yol. XXXI, p. 135 (Feb. 15, 1884); and the 
reports of the various State Geological Surveys, and the com¬ 
missioners of the various State capitols and of other public 
buildings. 

By way of comparison the following reports of tests of building 
stones of Great Britain may be interesting: Proceedings of the 
Institute of Civil Engineers, Yol. CVII (1891-92), pp. 341-69; 
abstract of the above, Engineering Neivs , Vol. XXVIII, pp. 279-82 
(Sept. 22, 1892). 

In consulting the above references or in using the results, the 
details of the manner of making of the experiments should be 
kept clearly in mind, particularly the method of preparing and 
bedding the specimen. 


4. Durability. 

19. “ Although the art of building has been practiced from the 
earliest times, and constant demands have been made in every age 
for the means of determining the best materials, yet the process of 
ascertaining the durability of stone appears to have received but 
little definite scientific attention, and the processes usually employed 
for solving this question are still in a very unsatisfactory state. 
Hardly any department of technical science is so much neglected as 
that which embraces the study of the nature of stone, and all the 
varied resources of lithology in chemical, microscopical, and physical 
methods of investigation, wonderfully developed within the last 



16 


NATURAL STONE. 


[CHAP. I. 


quarter century, have never yet been properly applied to the selec¬ 
tion and protection of stone used for building purposes/’* 

Examples of the rapid decay of building stones have already been 
referred to, and numerous others could be cited, in which a stone 
which it was supposed would last forever has already begun to 
decay. In every way, the question of durability is of more interest 
to the architect than to the engineer ; although it is of enough 
importance to the latter to warrant a brief discussion here. 

20. Destructive Agents. The destructive agents may be clas¬ 
sified as mechanical, chemical, and organic. The last are unim¬ 
portant, and will not be considered here. 

21. Mechanical Agents. For our climate the mechanical agents 
are the most efficient. These are frost, wind, rain, fire, pressure, 
and friction. 

The action of frost is usually one of the main causes of rapid 
decay. Two elements are involved,—the friability of the material 
and its power of absorbing moisture. In addition to the alter¬ 
nate freezing and thawing, the constant variations of temperature 
from day to day, and even from hour to hour, give rise to molecular 
motions which affect the durability of stone as a building material. 
This effect is greatest in isolated columns,—as monuments, bridge 
piers, etc. 

The effect of rain depends upon the solvent action of the gases 
which it contains, and upon its mechanical effect in the wear of 
pattering drops and streams trickling down the face of the wall. 

A gentle breeze dries out the moisture of a building stone and 
tends to preserve it; but a violent wind wears it away by dashing 
sand grains, street dust, ice particles, etc., against its face. The 
extreme of such action is illustrated by the vast erosion of the sand¬ 
stone in the plateaus of Colorado, Arizona, etc., into tabular mesas , 
isolated pillars, and grotesquely-shaped hills, by the erosive force of 
sand grains borne by the winds. The effect is similar to that of the 
sand blast as used in various processes of manufacture. A violent 
wind also forces the rain-water, with all the corrosive acids it con¬ 
tains, into the pores of stones, and carries off the loosened grains, 
thus keeping a fresh surface of the stone exposed. Again, the 
swaying of tall edifices by the wind must cause a continual motion, 


* Tenth Census of the U. S., Vol. X., Report on the Quarry Industry, p. 364. 








ART. 2 .] 


DURABILITY OF BUILDING STORES. 


17 


not only in the joints between the blocks, but among the grains of 
the stones themselves. Many of these have a certain degree of 
flexibility, it is true; and yet the play of the grains must gradually 
increase, and a tendency to disintegration result. 

Experience in great fires in the cities shows that there is no 
stone which can withstand the fierce heat of a mass of burning 

o 

buildings. Sandstones seem to be the least affected by great heat, 
and granite most. 

Friction affects sidewalks, pavements, etc., and has already 
been referred to (§ 8). It would also affect bridge piers, sea-walls, 
docks, etc. 

The effect of pressure in destroying stone is one of the least 
importance, provided the load to be borne does not too nearly equal 
the crushing strength. The pressure to which stone is subjected 
does not generally exceed one tenth of the ultimate strength as 
determined by methods already described. 

22. Chemical Agents. The principal ones are acids. Every 
constituent of stone, except quartz, is subject to attack by acids; 
and the carbonates, which enter as chief constituents or as cement¬ 
ing materials, yield very readily to such action. Oxygen and am¬ 
monia by their chemical action tend to destroy stones. In cities or 
manufacturing districts sulphur acids and carbonic acid have a 
very marked effect. These all result from the combustion of gas, 
coal, etc., and some are also the residuary gases of many kinds of 
manufactories. The nitric acid in the rain and the atmosphere 
exerts a perceptible influence in destroying building stone. 

23. Resisting Agents. The durability of a building stone de¬ 
pends upon three conditions; viz., the chemical and mineralogical 
nature of its constituents, its physical structure, and the character 
and position of its exposed surfaces. 

24. Chemical Composition. The chemical composition of the 
principal constituent mineral and of the cementing material has an 
important effect upon the durability of a stone. 

A siliceous stone, other things being equal, is more durable than 
a limestone; but the durability of the former plainly depends upon 
the state of aggregation of the individual grains and their cement¬ 
ing 1 bond, as well as on the chemical relation of the silica to the 
other chemical ingredients. A dolomitic limestone is more durable 
than a pure limestone. 





18 


NATURAL STONE. 


[CHAP. I. 


A stone that absorbs moisture abundantly and rapidly is apt to 
be injured by alternate freezing and thawing; hence clayey constit¬ 
uents are injurious. An argillaceous stone is generally compact, 
and often has no pores visible to the eye; yet such will disintegrate 
rapidly either by freezing and thawing, or by corrosive vapors. 

The presence of calcium carbonate, as in some forms of marble 
and in earthy limestones, renders a building material liable to rapid 
attack by acid vapors. In some sandstones the cementing material 
is the hydrated form of ferric oxide, which is soluble and easily 
removed. Sandstones in which the cementing material is siliceous 
are likely to be the most durable, although they are not so easily 
worked as the former. A stone that has a high per cent, of alumina 
(if it be also non-crystalline), or of organic matter, or of protoxide 
of iron, will usually disintegrate rapidly. Such stones are gen¬ 
erally of a bluish color. 

25. Seasoning. The thorough drying of a stone before, and the 
preservation of this dryness after, its insertion in masonry are com¬ 
monly recognized as important factors of its durability; but the 
exact nature of the process of seasoning, and of the composition 
of the quarry-sap removed by thorough drying, have never been 
determined. The quarry w T ater may contain little else than ordinary 
well-water, or may be a solution more or less nearly saturated, at the 
ordinary temperature, with carbonate of calcium, silica, double salts 
of calcium and magnesium, etc. In the latter case, hardening re¬ 
sults from the drying, and an exact knowledge of its nature might 
throw important light on the best means for the artificial preserva¬ 
tion of stone. Again, water may exist in large quantity, in chemical 
combination, in the silicates (e.g., chlorite, kaolin, etc.), or in the 
hydrated iron oxides which constitute the cement of a building 
stone. 

26. Physical Structure. The physical properties which con¬ 
tribute to durability are hardness, toughness, homogeneity, con¬ 
tiguity of the grains, and the structure—whether crystalline or 
amorphous. 

Although hardness (resistance to crushing) is often regarded as 
the most important element, yet resistance to weathering does not 
necessarily depend upon hardness alone, but upon hardness and the 
non-absorbent properties of the stone. A hard material of close 
and firm texture is, however, in those qualities at least, especially 



ART. 2 .] 


DURABILITY OF BUILDING STONES. 


19 


fitted to resist friction, as in stoops, pavements, and road metal, and 
the wear of rain-drops, dripping rain-water, the blows of the waves, 
etc. 

Porosity is an objectionable element. An excessive porosity in¬ 
creases the layer of decomposition which is caused by the acids of 
the atmosphere and of the rain, and also deepens the penetration of 
frost and promotes its work of disintegration. 

If the constituents of a rock differ greatly in hardness, texture, 
solubility, porosity, etc., the weathering is unequal, the surface is 
roughened, and the sensibility of the stone to the action of frost is 
increased. 

The principle which obtains in applying an artificial cement, 
such as glue, in the thinnest film in order to secure the greatest 
binding force finds its analogy in the building stones. The thinner 
the films of the natural cement and the closer the grains of the pre¬ 
dominant minerals, the stronger and more durable the stone. One 
source of weakness in the famous brown-stone of New York City 
lies in the separation of the rounded grains of quartz and feldspar 
by a superabundance of ocherous cement. Of course the further 
separation produced by fissure, looseness of lamination, empty 
cavities and geodes, and excess of mica tends to deteriorate still 
further a weak building stone. 

Experience has generally shown that a crystalline structure re¬ 
sists atmospheric attack better than an amorphous one. This prin¬ 
ciple has been abundantly illustrated in the buildings of New York 
City. The same fact is generally true with the sedimentary rocks 
also, a crystalline limestone or good marble resisting erosion better 
than earthy limestone. A stone that is compactly and finely granular 
will exfoliate more easily by freezing and thawing than one that is 
coarse-grained. A stone that is laminar in structure absorbs mois¬ 
ture unequally and will be seriously affected by unequal expansion 
and contraction,—especially by freezing and thawing. Such a stone 
will gradually separate into sheets. A stone that has a granular 
texture, as contrasted with one that is crystalline or fibrous, will 
crumble sooner by frost and by chemical agents, because of the 
easy dislodgment of the individual grains. 

The condition of the surface, whether rough or polished, in¬ 
fluences the durability,—the smoother surface being the better„ 



20 


NATURAL STONE. 


[CHAP. I. 


The stone is more durable if the exposed surface is vertical than if 
iucliued. The lamination of the stone should be horizontal. 

27. Methods of Testing Durability. It has long been recog¬ 
nized that there are two ways in which we can form a judgment of 
the durability of a building stone, and these may be distinguished 
as natural and artificial. 

28. Natural Methods. These must always take the precedence 
whenever they can be used, because they involve (1) the exact 
agencies concerned in the atmospheric attack upon stone, and (2) 
long periods of time far beyond the reach of artificial experiment. 

One method is to visit the quarry and observe whether the ledges 
that have been exposed to the weather are deeply corroded, or 
whether these old surfaces are still fresh. In applying this test, 
consideration must be given to the modifying effect of geological 
phenomena. It has been pointed out that “the length of time the 
ledges have been exposed, and the changes of actions to which 
they may have been subjected during long geological periods, are 
unknown; and since different quarries may not have been exposed 
to the same action, they do not always afford definite data for re¬ 
liable comparative estimates of durability, except where different 
specimens occur in the same quarry.” 

North of the glacial limit, all the products of decomposition 
have been planed away and deposited as drift-formation over the 
length and breadth of the land. The rocks are therefore, in gen¬ 
eral, quite fresh in appearance, and possess only a slight depth of 
cap or worthless rock. The same classes of rock, however, in the 
South are covered with rotten products from long ages of atmos¬ 
pheric action. 

A study of the surfaces of old buildings, bridge piers, monu¬ 
ments, tombstones, etc., which have been exposed to atmospheric 
Influences for years, is one of the best sources of reliable information 
concerning the durability of stone. A durable stone will retain the 
tool-marks made in working it, and preserve its edges and corners 
sharp and true. 

29. Artificial Methods of Testing Durability. The older but 
less satisfactory methods are: determining (1) the resistance to 
crushing, (2) the absorptive power, (3) the resistance to the expan¬ 
sion of frost, by saturating the stone with some solution which will 
crystallize in the pores of the stone and produce an effect similar to 
-frost, (4) the solubility in acids, and (5) microscopical examination. 







J\KT. 2 .] DURABILITY OF BUILDING STONES. 21 

30. Absorptive Power. The ratio of absorption depends largely 
on the density,—a dense stone absorbing less water than a lighter, 
more porous one. Compactness is therefore a matter of impor¬ 
tance, especially in cold climates; for if the water in a gtone is once 
allowed to freeze, it destroys the surface, and the stone very speedily 
crumbles away. Other things being equal, the less the absorption 
the better the stone. 

To determine the absorptive power, dry the specimen and weigh 
it carefully; then soak it in water for 24 hours, and weigh again. 
The increase in weight will be the amount of absorption. Table 4 
shows the weight of water absorbed by the stone as compared with 
the weight of the dry stone—that is, if 300 units of dry stone weigh 
301 units after immersion, the absorption is 1 in 300, and is recorded 
as 1-300. 

Dr. Hiram A. Cutting, State Geologist of Vermont, determined 
the absorptive power * by placing the specimens in water under the 
receiver of an air-pump, and found the ratio of absorption a little 
larger than is given in the following table. It is believed that the 
results given below more nearly represent the conditions of actual 
practice. The values in the “Max.” column are the means of two 
or three of the largest results, and those in the “Min.” column of 
two or three of the smallest. The value in the last column is the 
mean for 20 or more specimens. 


TABLE 5. 

Absorptive Power of Stone, Brick, and Mortar. 


Kind of Material. 

Ratio of Absorption. 

Max. 

Min. 

Average. 

.fi-rnnitps . 

1-150 

0 

1-750 

MnrBlps ... 

1-150 

0 

1-300 

FiimDStOTIfiS.... 

1-20 

1-500 

1-38 

!4rmrlstrmp.s... 

1-15 

1-240 

1-24 

Bricks.,.. 

1-4 

1-50 

1-10 

Mortars. 

1-2 

1-10 

1-4 






31. Effect of Frost. To determine the probable effect of frost 
upon a stone, carefully wash, dry, and weigh samples, and then wet 


* Van Nostrand’s Engin’g Mag., vol. xxiv. pp. 491-95. 




























22 


NATURAL STONE. 


[CHAP. I. 


them and expose to alternate freezing and thawing, after which 
wash, dry, and weigh again. The loss in weight measures the rela¬ 
tive durability. 

A quicker way of accomplishing essentially the same result is to 
heat the specimens to 500° or 600 J F., and plunge them, while hot, 
into cold water. The following comparative results were obtained 
by the latter method : * 

Relative Ratio of Loss. 


White brick. 1 

Rechbrick. 2 

Brown-stone (sandstone from Conn.).... 5 

Nova Scotia sandstone. 14 


32. Brard’s Test. Brard’s method of determining the effect of 
frost is much used, although it does not exactly conform to the con¬ 
ditions met with in nature. It consists in weighing carefully some 
small pieces of the stone, which are then boiled in a concentrated 
solution of sulphate of soda and afterwards hung up for a few days 
in tlie open air. The salt crystallizes in the pores of the stone, 
expands, and produces an effect somewhat similar to frost, as it 
causes small pieces to separate in the form of dust. The specimens 
are again weighed, and those which suffer the smallest loss of weight 
are the best. The test is often repeated several times. It will be 
seen that this method depends upon the assumption that the action 
of the salt in crystallizing is similar to that of water in freezing. 
This is not entirely correct, since it substitutes chemical and 
mechanical action for merely mechanical, to disintegrate the stone, 
thus giving the specimen a worse character than it really deserves. 
The following results were obtained by this method: f 

Relative Ratio of Loss. 


Hard brick. 1 

Light dove-colored sandstone from Seneca, Ohio- 2 

Coarse-grained sandstone from Nova Scotia. 2 

Coarse-grained sandstone from Little Falls, N. J. 5 

Coarse dolomite marble from Pleasantville, N. Y.... 7 

Coarse-grained sandstone from Conn. 13 

Soft brick. 16 

Fine-grained sandstone from Conn. 19 


* Tenth Census of the U. S., vol. x., Report on the Quarry Industry, p. 384. For 
E table showing essentially the same results, see Van Nostrand’s Engin’g Mag., voL 
xiv. p. 537. 

t Tenth Census, vol. x., Report of the Quarry Industry, p. 385. 















ART. 2.] 


DURABILITY OF BUILDING STONES. 


9Q 

rw O 


33. Effect of the Atmosphere. To determine the effect of the 
atmosphere of a large city, where coal is used for fuel, soak clean 
small pieces of the stone for several days in water which contains one 
per cent, of sulphuric and hydrochloric acids, agitating frequently. 
If the stone contains any earthy matter likely to be dissolved by the 
gases of the atmosphere, the water will be more or less cloudy or 
muddy. The following results were obtained by this method: * 

Relative Ratio of Loss. 


White brick... 1 

Red brick. 5 

Nova Scotia stone. 9 

Brown-stone. 30 


34. Microscopical Examination. It is now held that the best 
method of determining the probable durability of a building stone 
is to study its surface, or thin, transparent slices, under a micro¬ 
scope. This method of study in recent years has been most fruit¬ 
ful in developing interesting and valuable knowledge of a scientific 
and truly practical character. An examination of a section by means 
of the microscope will show, not merely the various substances which 
compose it, but also the method according to which they are 
arranged and by which they are attached to one another. For 
example, pyrites is considered to be the enemy of the quarryman 
and constructor, since it decomposes Avith ease, and stains and dis¬ 
colors the rock. Pyrites in sharp, Avell-defined crystals sometimes 
decomposes with great difficulty. If a crystal or grain of pyrites is 
embedded in soft, porous, light-colored sandstones, like those which 
come from Ohio, its presence will Avith certainty soon demonstrate 
itself by the black spot which will form about it in the porous 
stone, and which will permanently .disfigure and mar its beauty. 
If the same grain of pyrites is situated in a very hard, compact, non¬ 
absorbent stone, the constituent minerals of which are not rifted or 
cracked, this grain of pyrites may decompose and the products be 
washed away, leaving the stone untarnished. ” 

35. Methods of Preserving. Vitruvius, the Roman architect, 
tAvo thousand years ago recommended that stone should be quamed 
in summer Avhen driest, and that it should be seasoned by being 
allowed to lie tAvo years before being used, so as to allow the natural 


* Tenth Census, vol. x., Report on the Quarry Industry, p. 385. 











24 


NATURAL STONE. 


[CHAP. I. 


sap to evaporate. It is a notable fact, that in the erection of St 
Paul’s Cathedral in London, England, Sir Christopher Wren re¬ 
quired that the stone, after being quarried, should be exposed for 
three years on the sea-beach, before its introduction into the 
building. 

The surfaces of buildings are often covered with a coating of 
paint, coal-tar, oil, paraffine, soap and alum, rosin, etc., to preserve 
them. 

Another method of treatment consists in bathing the stone in 
successive solutions, the chemical actions bringing about the forma¬ 
tion of insoluble silicates in the pores of the stone. For example, if 
a stone front is first washed with an alkaline fluid to remove dirt, 
and this followed by a succession of baths of silicate of soda or 
potash, and the surface is then bathed in a solution of chloride of 
lime, an insoluble lime silicate is formed. The soluble salt is then 
washed away, and the insoluble silicate forms a durable cement and 
checks disintegration. If lime-water is substituted for chloride of 
lime, there is no soluble chloride to wash away. 

There are a great many applications that have been used for the 
prevention of the decay of building stones, as paint, oil, coal-tar, 
bees-wax, rosin, paraffine, etc., and numerous chemical preparations 
similar to that mentioned in the paragraph just above; but all are 
expensive, and none have proved fairly satisfactory. * 

It has already been stated that, in order to resist the effects of 
both pressure and weathering, a stone should' be placed on its nat¬ 
ural bed. This simple precaution adds considerably to the dura¬ 
bility of any stone. 

Art. 3, Classification and Description of Building Stones. 

36. Classification. Building stones are variously classified 
according to geological position, physical structure, and chemical 
composition. 

37. Geological Classification. The geological position of rocks 
nas but little connection with their properties as building materials. 
As a general rule, the more ancient rocks are the stronger and the 

* For an elaborate and valuable article by Prof. Eggleston on the causes of decay 
and the methods of preserving building stones, see Trans. Am. Soc. of C. E., vol. 
xv. pp. 647-704; and for a discussion on the same, see same volume, pp. 705-16. 





AMT. 3 .] 


DESCRIPTION OF BUILDING STONES. 


25 


more durable ; but to this there are many exceptions. According 
to the usual geological classification, rocks are divided into igneous, 
metamorpliic, and sedimentary. Greenstone, basalt, and lava are 
examples of igneous rocks ; granite, marble, and slate, of meta- 
morphic ; and sandstone, limestone, and clay, of sedimentary. Al¬ 
though clay can hardly be classed with building stones, it is not 
entirely out of place in this connection, since it is employed in 
making bricks and cement, which are important elements of 
masonry. 

38. Physical Classification. With respect to the structural 
character of large masses, rocks are divided into stratified and un¬ 
stratified. 

In their more minute structure the inistratified rocks present, 
for the most part, an aggregate of crystalline grains, firmly adhering 
together. Granite, trap, basalt, and lava are examples of this class* 

In the more minute structure of stratified rocks, the following 
Varieties are distinguished : 1 . Compact crystalline structure; ac¬ 
companied by great strength and durability, as in quartz-rock and 
marble. 2. Slaty structure, easily split into thin layers; accom¬ 
panied by both extremes of strength and durability, clay-slate and 
hornblende-slate being the strongest and most durable. 3. The 
granular crystalline structure, in which crystalline grains either 
adhere firmly together, as in gneiss, or are cemented into one mass 
by some other material, as in sandstone ; accompanied by all degree? 
of compactness, porosity, strength, and durability, the lowest ex. 
treme being sand. 4. The compact granular structure, in which 
the grains are too small to be visible to the unaided eye, as in blue 
limestone ; accompanied by considerable strength and durability. 
5. Porous , granular structure, in which the grains are not crystal¬ 
line, and are often, if not always, minute shells cemented together; 
accompanied by a low degree of strength and durability. 6. The 
conglomerate structure, where fragments of one material are embed¬ 
ded in a mass of another, as graywacke; accompanied by all degrees 
of strength and durability. 

A study of the fractured surface of a stone is one means of 
determining its structural character. The even fracture, when the 
surfaces of division are planes in definite positions, is characteristic 
of a crystalline structure. The uneven fracture, when the broken 
surface presents sharp projections, is characteristic of a granular 



26 


NATURAL STONE. 


[CHAP. I. 


structure. The slaty fracture gives an even surface for planes of 
division parallel to the lamination, and uneven for other directions 
of division. The conchoidal fracture presents smooth concave and 
convex surfaces, and is characteristic of a hard and compact struct¬ 
ure. The earthy fracture leaves a rough, dull surface, and indi¬ 
cates softness and brittleness. 

39. Chemical Classification. Stones are divided into three 
classes with respect to their chemical composition, each distin¬ 
guished by the earth which forms its chief constituent; viz., sili¬ 
ceous stones, argillaceous stones, and calcareous stones. 

Siliceous Stones are those in which silica is the characteristic earthy 
constituent. With a few exceptions their structure is crystalline- 
granular, and the crystalline grains contained in them are hard and 
durable ; hence weakness and decay in them generally arise from 
the decomposition or disintegration of some softer and more perish¬ 
able material, by which the grains are cemented together, or, when 
they are porous, by the freezing of water in their pores. The prin¬ 
cipal siliceous stones are granite, syenite, gneiss, mica-slate, green¬ 
stone, basalt, trap, porphyry, quartz-rock, hornblende-slate, and 
sandstone. 

Argillaceous or Clayey Stones are those in which alumina, although 
it may not always be the most abundant constituent, exists in suf¬ 
ficient quantity to give the stone its characteristic properties. The 
principal kinds are slate and gravwacke-slate. 

Calcareous Stones are those in which carbonate of lime pre¬ 
dominates. They effervesce with the dilute mineral acids, which 
combine with the lime and set free carbonic acid gas. Sulphuric 
acid forms an insoluble compound with the lime. Nitric and mu¬ 
riatic acids form compounds with it, which are soluble in water. 
By the action of intense heat the carbonic acid is expelled in gas¬ 
eous form, and the lime is left in its caustic or alkaline state, when 
it is called quicklime. Some calcareous stones consist of pure car¬ 
bonate of lime ; in others it is mixed with sand, clay, and oxide 
of iron, or combined with carbonate of magnesia. The durability 
of calcareous stones depends upon their compactness, those which 
are porous being disintegrated by the freezing of water, and by the 
chemical action of an acid atmosphere. They are, for the most 
part, easily wrought. The principal calcareous stones are marble. 



AIIT. 3.] 


DESCRIPTION OF BUILDING STONES. 


07 

'v I 


compact limestone, granular limestone (the calcareous stone of the 
geological classification), and magnesian limestone or dolomite. 

40. Description of Building Stones. A few of the more 
prominent classes of building stones will now be briefly described. 

41. Trap. Although trap is the strongest of building materials, 
and exceedingly durable, it is little used, owing to the great difti- 
culty with which it is quarried and wrought. It is an exceedingly 
tough rock, and, being generally without cleavage or bedding, is 
especially intractable under the hammer or chisel. It is, however, 
sometimes used with excellent effect in cyclopean architecture, the 
blocks of various shapes and sizes being fitted together with no 
effort to form regular courses. The “ Palisades” (the bluff skirting 
the western shore of the Hudson River, opposite and above New 
York) are composed of trap-rock,—much used for road-metal, street 
pavements, and railroad ballast. 

42. Granite. Granite is the strongest and most durable of all 
the stones in common use. It generally breaks with regularity, 
and may be quarried in simple shapes with facility ; but it is ex¬ 
tremely hard and tough, and therefore can only be wrought into 
elaborate forms with a great expenditure of labor. For this reason 
the use of granite is somewhat limited. Its strength and durability 
commend it, however, for foundations, docks, piers, etc., and for 
massive buildings; and for these purposes it is in use the world 
over. 

The larger portion of our granites are some shade of gray in 
color, though pink and red varieties are not uncommon, and black 
varieties occasionally occur. They vary in texture from very fine 
and homogeneous to coarsely porphyritic rocks, in which the indi¬ 
vidual grains are an inch or more in length. Excellent granites are 
found in New England, throughout the Alleghany belt, in the 
Rocky Mountains, and in the Sierra Nevada. Very large granite 
quarries exist at Vinalhaven, Maine ; Gloucester and Quincy, Mas¬ 
sachusetts; and at Concord, New Hampshire. These quarries fur¬ 
nish nearly all the granite used in this country. An excellent 
granite, which is largely used at Chicago and in the Northwest, is 
found at St. Cloud, Minnesota. 

At the Vinalhaven quarry a single block 300 feet long, 20 feet 
wide, and 6 to 10 feet thick was blasted out, being afterwards broken 
up. Until recently the largest single block ever quarried and 




28 


NATURAL STONE. 


[CHAP. I. 


dressed in this country was that used for the General Wool Monu¬ 
ment, now in Troy, New York, which measured, when completed, 
60 feet in height by 5J feet square at the base, being only 9 feet 
shorter than the Egyptian Obelisk now in Central Park, New York. 
In 1887 the Bodwell Granite Company took out from its quarries in 
Maine a granite shaft 115 feet long, 10 feet square at the base, and 
weighing 850 tons. It is claimed that this is the largest single 
quarried stone on record. 

43. Marbles. In common language, any limestone which will take 
a good polish is called a marble ; but the name is properly applied 
only to limestones which have been exposed to metamorphic action, 
and have thereby been rendered more crystalline in texture, and 
have had their color more or less modified or totally removed. 
Marbles exhibit great diversity of color and texture. They are- 
pure white, mottled white, gray, blue, black, red, yellow, or mot¬ 
tled with various mixtures of these colors. Marble is confessedly 
the most beautiful of all building materials, but is chiefly employed 
for interior decorations. 

44. Limestones. Limestones are composed chiefly or largely of 
carbonate of lime. There are many varieties of limestone, which 
differ in color, composition, and value for engineering and building 
purposes, owing to the differences in the character of the deposits 
and chemical combinations entering into them. “If the rock is 
compact, fine-grained, and has been deposited by chemical agencies, 
w r e have a variety of limestone known as travertine. If it contains 
much sand, and has a more or less conchoidal fracture, we have a 
siliceous limestone. If the silica is very fine-grained, it is horn- 
stone. If the silica is distributed in nodules or flakes, either in 
seams or throughout the mass, it is cherty limestone; if it contains 
silica and clay in about equal proportions, hydraulic limestone ; if 
clay alone is the principal impurity, argillaceous limestone ; if iron 
is the principal impurity, ferruginous limestone ; if iron and clay 
exceed the lime, ironstone. If the ironstone is decomposed, and 
the iron hydrated, it is rottenstone; if carbonate of magnesia forms 
one third or less, magnesian limestone ; if carbonate of magnesia 
forms more than one third, dolomitic limestone.” 

The lighter-colored and fine-grained limestones, when sawed and 
used as ashlars, are deservedly esteemed as among our best building 
materials. I hey are, however, less easily and accurately worked 



ART. 3.] 


DESCRIPTION OF BUILDING STONES. 


2S> 


under the chisel than sandstones, and for this reason and their 
greater rarity are far less generally used. The gray limestones, liko 
that of Lockport, New York, when hammer-dressed, have the ap¬ 
pearance of light granite, and, since they are easily wrought, they 
are advantageously used for trimmings in buildings of brick. 

Some of the softer limestones possess qualities which specially 
commend them for building materials. For example, the cream- 
colored limestone of the Paris basin (ccdcaire grossier) is so soft that 
it may be dressed with great facility, and yet hardens on exposure, 
and is a durable stone. Walls laid up of this material are frequently 
planed down to a common surface, and elaborately ornamented at 
small expense. The Topeka stone, found and now largely used in 
Kansas, has the same qualities. It may be sawed out in blocks 
almost as easily as wood, and yet is handsome and durable when 
placed in position. The Bermuda stone and coquina are treated in 
the same way. 

Large quantities of limestones and dolomites are quarried in 
nearly all of the Western States. These are mostly of a dull grayish 
color, and their uses are chiefly local. The light-colored oolitic 
limestone of Bedford, Indiana, is, however, an exception to this, 
rule. Not only are the lasting qualities fair and the color pleasing, 
but its fine even grain and softness render it admirably adapted for 
carved work. It has been very widely used within the last few 
years. This stone is often found in layers 20 and 30 feet thick, and 
is much used for bridge piers and other massive work. There are 
noted limestone quarries at Dayton and Sandusky, Ohio; at Bedford, 
Ellettsville, and Salem, Indiana; at Joliet, Lemont, Grafton, and 
Chester, Illinois; and at Cottonwood, Kansas. 

45. Sandstones. “Sandstones vary much in color and fitness for 
architectural purposes, but they include some of the most beautiful, 
durable, and highly valued materials used in construction. What¬ 
ever their differences, they have this in common, that they are 
chiefly composed of sand—that is, grains of quartz—to a greater or 
less degree cemented and consolidated. They also frequently con¬ 
tain other ingredients, as lime, iron, alumina, manganese, etc., by 
which the color and texture are modified. Where a sandstone is 
composed exclusively of grains of quartz, without foreign matter, it 
may be snow-white in color. Examples of this variety are known 
in many localities. They are rarely used for building, though capa- 



30 


NATURAL STONE. 


[CHAP. T. 


ble of being employed for that purpose with excellent effect. They 
have been more generally valued as furnishing material for the man¬ 
ufacture of glass. The color of sandstones is frequently bright and 
handsome, and constitutes one of the many qualities which have 
rendered them so popular. It is usually caused by iron; when gray, 
blue, or green, by the protoxide, as carbonate or silicate ; when 
brown, by the hydrated oxide ; when red, by the anhydrous oxide. 
The purple sandstones usually derive this shade of color from a 
small quantity of manganese. 

“The texture of sandstones varies with the coarseness of the 
sand of which they are composed, and the degree to which it is con¬ 
solidated. Usually the material which unites the grains of sand 
is silica; and this is the best of all cements. This silica has been 
deposited from solution, and sometimes fills all the interstices be¬ 
tween the grains. If the process of consolidation has been carried 
far enough, or the quartz grains have been cemented by fusion, the 
sandstone is converted into quartzite,—one of the strongest and most 
durable of rocks, but, in the ratio of its compactness, difficult to 
work. Lime and iron often act as cements in sandstones, but both 
are more soluble and less strong than silica. Hence the finest and 
most indestructible sandstones are such as consist exclusively of 
grains of quartz united by siliceous cement. In some, sandstones 
part of the grains are fragments of feldspar, and these, being liable 
to decomposition, are elements of weakness in the stone. The very 
fine-grained sandstones often contain a large amount of clay, and 
thus, though very handsome, are generally less strong than those 
which are more purely siliceous. 

“ The durability of sandstones varies with both their physical 
and chemical composition. When nearly pure silica and well ce¬ 
mented, sandstones are as resistant to weather as granite, and very 
much less affected by the action of fire. Taken as a whole, they 
may be regarded as among the most durable of building materials. 
YV hen first taken from the quarry, and saturated with quarry water 
{a weak solution of silica), they are frequently very soft, but on ex¬ 
posure become much harder by the precipitation of the soluble silica 
contained in them. 

46. “Since they form an important part of all the groups of 
sedimentary rocks, sandstones are abundant in nearly all countries; 
and as they are quarried with great ease, and are wrought with the 





ART. 3.] 


DESCRIPTION OF BUILDING STONES. 


31 


hammer and chisel with much greater facility than limestones* 
granites, and most other kinds of rocks, these qualities, joined to 

their various and pleasant colors and their durability, have made 

» 

them the most popular and useful of building stones. In the 
United States we have a very large number of sandstones which are 
extensively used for building purposes. 

“ Among these may be mentioned the Dorchester stone of New 
Brunswick, and Broivn-stone of Connecticut and New Jersey. 
These have been much used in the buildings of the Atlantic cities. 
The latter has been very popular, but experience has shown it to be 
seriously lacking in durability. 

“ Among the sandstones most frequently employed in the build¬ 
ing of the interior are :— 

1. <tf The Ohio stone , derived from the Berea grit, a member of 
the Lower Carboniferous series in Northern Ohio. The principal 
quarries are located at Amherst and Berea. The stone from Am¬ 
herst is generally light drab in color, very homogeneous in texture, 
and composed of nearly pure silica. It is, very resistant to fire and 
weathering, and is, on the whole, one of the best and handsomest 
building stones known. The Berea stone is lighter in color than 
the Amherst, but sometimes contains sulphide of iron, and is then 
liable to stain and decompose. 

2. <s The Waverly sandstone, also derived from the Lower Car¬ 
boniferous series, comes from Southern Ohio. This is a fine¬ 
grained homogeneous stone of a light-drab or dove color, works with 
facility, and is very handsome and durable. It forms the material 
of which many of the finest buildings of Cincinnati are constructed, 
and is, justly, highly esteemed there and elsewhere. 

3. “ The Lake Superior sandstone is a dark, purplish-brown 
stone of the Potsdam age, quarried at Bass Island, Marquette, etc. 
This is rather a coarse stone, of medium strength, but homogeneous 
and durable, and one much used in the Lake cities. 

4. “ The St. Genevieve stone is a fine-grained sandstone of a del¬ 
icate drab or straw color, very homogeneous in tone and texture. 
It is quarried at St. Genevieve, Missouri, and is one of the hand¬ 
somest of all our sandstones. 

5. “ The Medina sandstone , which forms the base of the Upper 
Silurian series in Western New York, furnishes a remarkably strong 



32 


NATURAL STONE. 


[CHAP. I. 


-•and durable stone, much used for pavement and curbing in the 
Lake cities. 

G. “ The coal-measures of Pennsylvania, Ohio, and other Western 
^States supply excellent sandstones for building purposes at a large 
number of localities. These vary in color from white to dark red 
or purple, though generally gray or drab. While strong and 
durable, they are mostly coarser and less handsome than the sand¬ 
stones which have been enumerated above. This is the source from 
which are derived the sandstones used in purely engineering struct¬ 
ures.”* 

47 . Other Names. There is a great variety of names of more 
or less local application, derived from the appearance of the stone, 
the use to which it is put, etc., which it would be impossible to 
•classify. The same stone often passes under entirely different 
names in different localities; and stones entirely different in their 
essential characteristics often pass under the same name. 

48 . Location of Quarries. For information concerning the 
location of quarries, character of product, etc., see: Tenth Census 
of the U. S., Yol. X, Report on Quarry Industry, pp. 107-363; 
Report of Smithsonian Institution, 1885-86, Part II, pp. 357-488; 
Merrill’s Stones for Building and Decoration, pp. 45-312—substan¬ 
tially the same as the preceding—and the reports of the various 
•State geological surveys. 

49 . Cost. See 88 226-38. 


* Prof. J. S. Newberry. 


I 





CHAPTER II. 


BRICK. 

51. Brick is made by submitting clay, which has been prepared 
properly and moulded into shape, to a temperature which converts 
it into a semi-vitrified mass. 

Common brick is a most valuable substitute for stone. Its 
comparative cheapness, the ease with which it is transported and 
handled, and the facility with which it is worked into structures of 
any desired form, are its valuable characteristics. It is, when prop¬ 
erly made, nearly as strong as the best building stone. It is but 
slightly affected by change of temperature or of humidity; and is 
also lighter than stone. 

Notwithstanding the good qualities which recommend brick as 
a substitute for stone, it is very little used in engineering structures. 
It is employed in the construction of sewers and bridge piers, and 
for the lining of tunnels. Brick could many times be profitably 
substituted for iron, stone, or timber in engineering structures. 
This is especially true since recent improvements in the process of 
manufacture have decreased the cost ivhile they have increased the 
quality and the uniformity of the product. The advantages of 
■employing brick-work instead of stone masonry will be discussed in 
connection with brick masonry in Chapter VIII. Probably one 
thing which has prevented the more general use of brick in engi¬ 
neering is the variable quality of the product and the trouble of 
proper inspection. 

52. Process of Manufacture. The Clay. The quality of the 
brick depends primarily upon the kind of clay. Common clays, of 
which the common brick is made, consist principally of silicate of 
alumina; but they also usually contain lime, magnesia, and oxide 
of iron. The latter ingredient is useful, improving the product by 
giving it hardness and strength; hence the red brick of the Eastern 
States is often of better quality than the white and yellow brick 
made in the West. Silicate of lime renders the clay too fusible, 

33 


34 


BRICK. 


[CHAP. II. 


and causes the bricks to soften and to become distorted in the pro¬ 
cess of burning. Carbonate of lime is certain to decompose in 
burning, and the caustic lime left behind absorbs moisture, prevents 
the adherence of the mortar, and promotes disintegration. 

Uncombined silica, if not in excess, is beneficial, as it preserves 
the form of the brick at high temperatures. In excess it destroys 
the cohesion, and renders the bricks brittle and weak. Twenty-five 
per cent, of silica is a good proportion. 

/ 53. Moulding. In the old process the clay is tempered with 
water and mixed to a plastic state in a pit with a tempering wheel, 
or in a primitive pug-mill; and then the soft, plastic clay is pressed 
into the moulds by hand. This method is so slow and laborious 
that it has been almost entirely displaced by more economical and 
expeditious ones in which the work is done wholly by machinery. 
There is a great variety of machines for }3reparing and moulding 
the clay, which, however, may be grouped into three classes, accord¬ 
ing to the condition of the clay when moulded: (1) soft-mud 
machines, for which the clay is reduced to a soft mud by adding 
about one quarter of its volume of water; (2) stiff-mud machines, 
for which the clay 's reduced to a stiff mud; and (3) dry-clay 
machines, with which the dry, or nearly dry, clay is forced into the 
moulds by a heavy pressure without having been reduced to a plastic 
mass. These machines may also be divided into two classes, accord¬ 
ing to the method of filling the moulds: (1) Those in which a con¬ 
tinuous stream of clay is forced from the pug-mill through a die 
and is afterwards cut up into bricks; and (2) those in which the 
clay is forced into moulds moving under the nozzle of the pug-mill. 

54. Burning. The time of burning varies with the character of 
the clay, the form and size of kiln, and the kind of fuel. With the 
older processes of burning, the brick, when dry enough, is built up 
in sections—by brick-makers called “arches,”—which are usually 
about 5 bricks (3J- feet) wide, 30 to 40 bricks (20 to 30 feet) deep, 
and from 35 to 50 courses high. Each section or “arch” has an 
opening—called an “eye”—at the bottom in the center of its width, 
which runs entirely through the kiln, and in which the fuel used in 
burning is placed. After the bricks are thus stacked up, the entire 
pile is enclosed with a wall of green brick, and the joints between 
the casing bricks are carefully stopped with mud. Burning, includ¬ 
ing drying, occupies from 6 to 15 days. The brick is first subjected 




CLASSIFICATIONS’ OF COMMONS BRICK. 


35 


to a moderate heat, and when all moisture has been expelled, the; 
heat is increased slowly until the “arch-brick,” i. e., those next to 
the “eye,” attain a white heat. This temperature is kept up until 
the burning is complete. Finally, all openings are closed, and the 
mass slowly cools. 

With the more modern processes of burning, the principal yards 
have permanent kilns. These are usually either a rectangular space 
surrounded, except for very wide doors at the ends, by permanent 
brick walls having fire-boxes on the outside; or the kiln may be. 
entirely enclosed—above as well as on the sides—with brick masonry. 
The latter are usually circular, and are sometimes made in com¬ 
partments, each of which has a separate entrance and independent 
connection with the chimney. The latter may be built within the 
kiln or entirely outside, but a downward draught is invariably 
secured. The fuel, usually fine coal, is placed near the top of the 
kiln, and the down draught causes a free circulation of the flame 
and heated gases about the material being burned. While some 
compartments are being fired others are being filled, and still 
others are being emptied. 

55. Fire Brick. Fire bricks are used whenever very high 
temperatures are to be resisted. They are made either of a very 
nearly pure clay, or of a mixture of pure clay and clean sand, or, in. 
rare cases, of nearly pure silica cemented with a small propoition 
of clay. The presence of oxide of iron is very injurious, and, as a 
rule, the presence of 6 per cent, justifies the rejection of the brick. 
In specifications it should generally be stipulated that fire brick 
should contain less than G per cent, of oxide of iron, and less than 
an aggregate of 3 per cent, of combined lime, soda, potash, and 
magnesia. The sulphide of iron—pyrites—is even worse in its 
effect on fire brick than the substances first named. 

When intended to resist only extremely high heat, silica should 
be in excess; and if to be exposed to the action of metallic oxides,, 
which would tend to unite with silica, alumina should be in excess. 

Good fire brick should be uniform in size, regular in shape,, 
homogeneous in texture and composition, easily cut, strong, and 
infusible. 

56. Classification of Common Brick. Bricks are classified 
according to (1) the way in which they are moulded; (2) their 
position in the kiln while being burned; and (3) their form or use,. 



36 


BRICK. 


[CHAP. II. 


1- The method of moulding gives rise to the following terms: 

Soft-mud Brick. One moulded from clay which has been reduced 
to a soft mud by adding water. It may be either hand-moulded or 
machine-moulded. 

Stiff-mud Brick. One moulded from clay in the condition of 
stiff mud. It is always machine-moulded. 

Pressed Brick. One moulded from dry or semi-dry clay. 

Re-pressed Brick. A soft-mud brick which, after being par¬ 
tially dried, has been subjected to an enormous pressure. It is 
also called, but less appropriately, pressed brick. The object of 
the re-pressing is to render the form more regular and to increase 
the strength and density. 

Slop Brick . In moulding brick by hand, the moulds are some¬ 
times dipped into water just before being filled with clay, to pre¬ 
vent the mud from sticking to them. Brick moulded by this 
process is known as slop brick. It is deficient in color, and has a 
comparatively smooth surface, with rounded edges and corners. 
This kind of brick is now seldom made. 

Sanded Brick. Ordinarily, in making soft-mud brick, sand is 
sprinkled into the moulds to prevent the clay from sticking; the 
brick is then called sanded brick. The sand on the surface is of no 
serious advantage or disadvantage. In hand-moulding, when sand 
is used for this purpose, it is certain to become mixed with the clay 
and occur in streaks in the finished brick, which is very undesira¬ 
ble ; and owing to details of the process, which it is here unneces¬ 
sary to explain, every third brick is especially bad. 

Machine-made Brick. Brick is frequently described as “ma¬ 
chine-made;” but this is very indefinite, since all grades and kinds 
are made by machinery. 

2. When brick was generally burned in the old-style up-draught 
kiln, the classification according to position was important; but 
with the new styles of kilns and improved methods of burning, the 
quality is so nearly uniform throughout the kiln, that the classifica¬ 
tion is less important. Three grades of brick are taken from the 
old-style kiln: 

Arch or Clmker Bricks. Those which form the tops and sides of 
the arches in which the fire is built. Being over-burned- and par¬ 
tially vitrified, they are hard, brittle, and weak. 



REQUISITES FOR GOOD BRICK. 


3 ? 


Body, Cherry, or Hard Bricks. Those taken from the interior 
of the pile. The best bricks in the kiln. 

Salmon, Pale, or Soft Bricks. Those which form the exterior of 
the mass. Being underburned, they are too soft for ordinary work, 
unless it be for filling. The terms salmon and pale refer to the 
color of the brick, and hence are not applicable to a brick made of 
a clay that does not burn red. Although nearly all brick clays burn 
red, yet the localities where the contrary is true are sufficiently 
numerous to make it desirable to use a different term in designating 
the quality. There is, necessarily, no relation between color, and 
strength and density. Brick-makers naturally have a prejudice 
against the term soft brick, which doubtless explains the nearly 
universal prevalence of the less appropriate term—salmon. 

C\ 3 • The form or use of bricks gives rise to the following classify 
cation:— 

Compass Brick. Those having one edge shorter than the other. 
Used in lining shafts, etc. 

Feather-edge Brick. Those of which one edge is thinner than 
the other. Used in arches ; and more properly, but less frequently, 
called voussoir brick. 

Face Brick. Those which, owing to uniformity of size and 
color, are suitable for the face of the wall of buildings. Sometimes 
face bricks are simply the best ordinary brick ; but generally the 
term is applied only to re-pressed or pressed brick made specially for 
this purpose. They are a little larger than ordinary bricks (§ 62). 

Sewer Brick. Ordinary hard brick, smooth, and regular in 
form. 

Paving Brick. Very hard, ordinary brick. A vitrified claj 
block, very much larger than ordinary brick, is sometimes used for 
paving, and is called a paving brick, but more often, and more 
properly, a brick paving-block. 

57. Requisites for Good Brick. 1. A good brick should have 
plane faces, parallel sides, and sharp edges and angles. 2. It should 
be of fine. Compact, uniform texture ; should be quite hard; and 
should give a clear ringing sound when struck a sharp blow. 3. It 
should not absorb more than one tenth of its weight of water. 4. 
Its specific gravity should be 2 or more. 5. The crushing strength 
of half brick, when ground flat and pressed between thick metaJ 





38 


BRICK. 


[CHAP. II. 


plates, should be at least 7,000 pounds per square inch. 6. Its mod¬ 
ulus of rupture should he at least 1,000 pounds per square inch. 

1. In regularity of form re-pressed brick ranks first, dry-clay 
brick next, then stiff-mud brick, and soft-mud brick last. Begu- 
larity of form depends largely upon the method of burning. 

2. The compactness and uniformity of texture, which greatly 
influence the durability of brick, depend mainly upon the method 
of moulding. As a general rule, hand-moulded bricks are best in 
this respect, since the clay in them is more uniformly tempered be¬ 
fore being moulded ; but this advantage is partially neutralized by 
the presence of sand seams (§ 56). Machine-moulded soft-mud 
bricks rank next in compactness and uniformity of texture. Then 
come machine-moulded stiff-mud bricks, which vary greatly in 
durability with the kind of machine used in their manufacture. 
By some of the machines, the brick is moulded in layers (parallel to 
any face, according to the kind of machine), which are not thor¬ 
oughly cemented, and which separate under the action of the frost. 
In compactness, the dry-clay brick comes last. However, the rela¬ 
tive value of the products made by the different processes varies 
with the nature ot the clay used. 

3. The absorptive power is one of the most important elements, 
since it greatly affects the durability of the brick, particularly its 
resistance to the effect of frost (see §§ 31 and 32). Very soft, un¬ 
der-burned brick will absorb from 25 to 33 per cent, of their weight 
of water. AVeak, light-red ones, such as are frequently used in fill¬ 
ing in the interior of walls, will absorb about 20 to 25 per cent.; 
while the best brick will absorb only 4 or 5 per cent. A brick may 
be called good which will absorb not more than 10 per cent. See 
Table 9 (page 45). 

4. The specific gravity of a brick does not indicate its quality, 
and depends mainly upon the amount of burning and the kind of 
fuel employed. Over-burned arch bricks, being both smaller and 
heavier than the better body bricks, have a considerably greater 
specific gravity, although inferior in quality. 

5. The crushing strength is not a certain index of the value of a 
brick, although it is always one of the items determined in testing 
brick—if a testing-machine is at hand. For any kind of service, 
the durability of a brick is of greater importance than its ability 
to resist crushing,—the latter is only remotely connected with dura- 



ABSORBING POWER. 


3ft 


bility. Tests of the crushing strength of individual bricks are use¬ 
ful only in comparing different kinds of brick, and give no idea of 
the strength of walls built of such bricks (see § 246). Furthermore, 
the crushing strength can not be determined accurately, since it 
varies greatlv with the size of the specimen and with the details of 
the experiments (see § 60). 

6. Owing to both the nature of the quality tested and the facility 
with which such a test can be made, the determination of the 
transverse strength is one of the best means of judging of the 
quality of a brick. The transverse strength depends mainly upon 
the toughness of the brick,—a quality of prime importance in bricks 
used for paving, and also a quality greatly affecting the resistance to 
frost. 

58. ABSORBING Power. The less the amount of water absorbed 
by a brick the greater, in all probability, will be its durability. 
The amount of water absorbed is, then, an important consideration 
:n determining the quality of a brick. There are different methods 
in use for determining the amount of water taken up by a brick, 
and these lead to slightly different results. Some experimenters dry 
the bricks in a hot-air chamber, while some dry them simply by ex¬ 
posing them in a dry room; some experimenters immerse the bricks 
in water in the open air, while others immerse them under the re¬ 
ceiver of an air-pump; some immerse whole brick, and some use 
small pieces; and, again, some dry the surface with bibulous paper, 
while others allow the surface to dry by evaporation. Air-drying 
most nearly represents the conditions of actual exposure in ma¬ 
sonry structures, since water not expelled in that way is in such a 
condition as not to do any harm by freezing. Immersion in the 
open air more nearly represents actual practice than immersion in 
a vacuum. The conditions of actual practice are best represented 
by testing whole brick, since some kinds have a more or less im¬ 
pervious skin. Drying the surface by evaporation is more accurate 
than drying it with paper; however, neither process is susceptible 
of mathematical accuracy. 

The absorbing power given in Table 9, page 45, was determined 
by (1) drying whole brick in a steam-heated room for three weeks, 
(2) weighing and (3) immersing them in water for forty-four 
hours; and then (4) drying for four hours—until all the water on 
the surface was evaporated,—and, finally, (5) again weighing them. 





40 


BRICK. 


[CHAP. II. 


The results in the table represent the mean of several observations. 
If the brick had been kiln-dried, or weighed before the surface- 
water was entirely removed, the apparent absorption would have 
been greater. 

Comparing the absorbing power of brick as given in the table 
on page 45 with that of stone on page 20, we see the absorbing 
power of the best brick is about equal to that of average lime¬ 
stone and sandstone, and much greater than marble and granite. 
For a method of rendering brick non-absorbent, see §§ 263-64. 

59. Transverse Strength. The experiments necessary to 
determine the transverse strength of brick are easily made (§ 16), 
give definite results, and furnish valuable information concerning 
the practical value of the brick; hence this test is one of the best in 
use. 

Table 6 gives the results of experiments made by the author on 
Illinois brick. The averages represent the results of from six to fifteen 


TABLE 6. 

Transverse Strength of Illinois Brick. 
(Summarized from Table 9, page 45.) 


Ref. 

No. 

Kind of Brick. 

Modulus of Rupture in 
Lbs. per Sq. In.* 

Co-efficient of Trans¬ 
verse Strength.* 

Max. 

Min. 

Average. 

Max. 

Min. 

Aver. 

1 

Soft - clay, hand - moulded, 
—best 50$ in kiln. 

2,233 

846 

1,409 

124 

47 

78 

2 

Soft-clay, machine-mould¬ 
ed,—best 50$ in kiln- 

2,354 

1,135 

1,712 

142 

63 

95 

3 

Stiff-clay, machine-mould¬ 
ed,—best 50$ in kiln.... 

1,475 

764 

1,114 

82 

42 

62 

4 

Dry-clay (pressed). 

495 

150 

336 

27 

8 

19 

5 

Secret Process. 

4,348 

2,235 

3,217 

241 

124 

178 


experiments on brick from three localities. The “Max.” and 
“Min.” columns contain the average of the two highest and the 
two lowest results respectively. 

The results in Table 7 were obtained under the direction of the 
Chief Engineer of the Lehigh Valley B. R. Each result represents. 


* For definition, see § 15. 































CRUSHING STRENGTH. 


41 


the mean of seven to nine experiments on bricks from different 
localities. The results in Table 6 are considerably greater than 


TABLE 7. 

Transverse Strength of Eastern Brick. 


Designation op Erick. 

Modulus of Rupture in 
Lbs. per Sq. In. 

Co-efficient of Trans¬ 
verse Strength. 

Max. 

Min. 

Average. 

Max. 

Min. 

Average. 

Very hard. 

1,790 

1,045 

1,852 

100 

58 

75 

Hard. 

944 

710 

805 

52 

39 

45 

Medium. 

645 

504 

597 

36 

28 

32 

Soft. 

444 

269 

378 

25 

15 

21 


those in Table 7, the difference being due probably more to recent 
improvements in the manufacture of brick and to the method of 
selection than to locality. The brick from which the results in 
Table 6 were derived were obtained from manufacturers well known 
for the high quality of their products. 

60. Crushing Strength. It has already been explained (§§ 7 
to 14) that the results for the crushing strength of stone vary 
greatly with the details of the experiments; but this difference is 
even greater in the case of brick than in that of stone. In testing 
stone the uniform practice is to test cubes (§ 10) whose faces are 
carefully dressed to parallel planes. In testing brick there is no 
settled custom. (1) Some experimenters test half brick while others 
test whole ones; (2) some grind the pressed surfaces accurately to 
planes, and some level up the surfaces by putting on a thin coat of 
plaster of Paris, while others leave them in the rough; and (3) some 
test the brick set on end, some on the side, and others laid flat¬ 
wise. 

1. From a series of experiments* on soft brick, the author con¬ 
cludes that the crushing strength per square inch of a quarter of a 
brick is about half that of a whole one; and that a half brick is 
about two thirds, and three quarters of a brick about five sixths, as 
strong per square inch as a whole one; or, in other words, the 
strength of a quarter, a half, and three quarters of a brick, and a 


* Engineering News, vol. xxi. p. 88. 





























BRICK. 


[CHAP. II. 


42 


whole one, are to each other as 3, 4, 5, and 6 respectively. The 
reason for this difference is apparent if a whole brick be conceived 
as being made up of a number of cubes placed side by side, in which 
case it is clear that the interior cubes will be stronger than the 
exterior ones because of the side support derived from the latter. 
For experiments showing the marked effect of this lateral support, 
see § 273. The quarter brick and the half brick have less of this 
lateral support than the whole one, and hence have correspondingly 
less crushing strength. 

2. The strength of the specimen will vary greatly with the degree 
of smoothness of its bed-surfaces. To determine the difference 
between reducing the pressed surfaces to a plane and leaving them 
in the rough, the author selected six bricks of regular form and 
apparently of the same strength, and tested three in the rough and 
the other three after having reduced the pressed surfaces to planes 
by laying on a coating of plaster of Paris, which, after drying, was 
ground off to a plane. The amount of plaster remaining on the 
surfaces was just sufficient to fill up the depressions. Both sets 
were tested in a hydraulic press between cast-iron, parallel (self- 
adjusting), pressing surfaces. The average strength of those that 
were plastered was 2.06 times the strength of those that were not 
plastered. This difference will vary with the relative strength of 
the brick and the plaster. The average strength of the bricks whose 
surfaces were plastered was 9,170 pounds per square inch, which is 
more than that of the plaster used; and therefore it is highly 
probable that if the surfaces had been reduced to planes by grind¬ 
ing, the difference in strength would have been still greater. See 
.also the last paragraph of § 12. 

3. As before stated, some experimenters test brick flatwise, some 
edgewise, and some endwise. Since bricks are generally employed 
in such a position that the pressure is on the broadest face, it seems 
a little more satisfactory to lay the brick flatwise while testing it; 
but since the only object in determining the crushing strength of 
brick is to ascertain the relative strength of different bricks,—the 
crushing strength of the brick is only remotely connected with the 
crushing strength of the brick-masonry (§ 246),—the position of the 
brick while being tested is not a matter of vital importance. Doubt¬ 
less the principal reason for testing them on end or edgewise is to 
bring them within the capacity of the testing-machine. However, 



CRUSHING STRENGTH. 


43 


there is one good reason against testing brick flatwise; viz., all 
homogeneous granular bodies fail under compression by shearing 
along planes at about 45° with the pressed surfaces, and hence if 
the height is not sufficient to allow the shearing stresses to act 
freely, an abnormal strength is developed. See also § 10. 

The relative strength of brick tested in the three positions—flat¬ 
wise, edgewise, and endwise—varies somewhat with the details of 
the experiments; but it is reasonably well settled that the strength 
of homogeneous brick flatwise between steel or cast-iron pressing 
surfaces is one and a half to two times as much as when the brick is 
tested on end. A few experiments by the author * seem to indicate 
that the strength edgewise is a little more than a mean between the 
■strength flatwise and endwise. If the brick is laminated (see para¬ 
graph 2, § 57), the relative strength for the three positions—flat¬ 
wise, edgewise, and endwise—will vary greatly with the direction of 
the grain. 

61. Comparatively few experiments have been made to deter¬ 
mine the strength of brick, and they are far from satisfactory, since 
the manner of making the experiment is seldom recorded. The 
■differences in the details of the experiments, together with the 
differences in the quality of the bricks themselves, are sufficient to 
cause a wide variation in the results obtained by different observers. 
The following data are given for reference and comparisons. 

The results in Table 8 (page 44) were made with the U. S. 
testing-machine at the Watertown (Mass.) Arsenal.f In each 
experiment the pressed surfaces were “ carefully ground flat and 
set in a thin facing of plaster of Paris, and then tested between steel 
pressing surfaces. ” 

The experiments given in Table 9 (page 45) were made by the 
author, on Illinois brick. The bricks were crushed between self- 
adjusting cast-iron pressing surfaces. Although No. 11 shows an 
average absorption, a moderate transverse strength, and a high crush¬ 
ing strength, this particular brand of brick disintegrated rapidly by 
the frost. This is characteristic of this class of brick, and is caused 
by the clay's being forced into the moulds or through the die in such a 
way as to leave the brick in laminae, not well cemented together. A 
critical examination of the brick with the unaided eye gave no indi- 


* Engineering News , vol. xxi. p. 88. 
t Compiled from the annual reports for 1883-85. 




Experiments on Brick with the Watertown Testing-machine. 


44 


BRICK 


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+ Samples of bricks used in Pension Building. See Tests of Metals, etc., 1883, p. 220. 

X Samples of bricks used in experimental brick piers (§246). See Tests of Metals, etc., 1883, pp. 217-19. 

§ Samples of bricks used iu experimental brick piers (§246). See Tests of Metals, etc., 1885, pp. 1138-61, 






































TABLE 9 

Absorptive Power, and Transverse and Compressive Strengths of Illinois Brick. 


CRUSHING STRENGTH. 


45 


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46 


BRICK. 


[CHAP. II. 


cation of a laminated structure, and yet compressing the brick in 
two positions—sidewise and edgewise—never failed to reveal such 
structure. The crushing strength in the table was obtained when 
the pressure was applied to the edges of the laminaB. In experi¬ 
ments Nos. 12,13, and 14 the pressed surfaces were so nearly mathe¬ 
matical planes that possibly these bricks stood more than they would 
have done if their beds had been jflastered. The strength of No. 15 
was beyond the capacity of the machine; a whole brick, on end, stood 
11,083 lbs. persq. in. without any cracks or snapping sounds—which 
usually occur at about half of the ultimate strength. 

Rankine says that “ strong red brick, when set on end, should 
require at least 1,100 lbs. per sq. in. to crush them; weak red ones, 
550 to 800 lbs. persq. in.; and fire bricks, 1,700 lbs. per. sq. in.”* * * § 
Experiments on the brick in general use in Berlin gave for 
“ ordinary” brick, on edge, a strength of 2,930 lbs. per sq. in.; and 
for “selected” brick, 3,670 lbs. per sq. in.f 

The brick used in the New York reservoir, when laid flat and 
packed with sand, showed an average strength, for four specimens, 
of 2,770 lbs. per sq. in.; and two samples tested between wood 
averaged 2,660 lbs. per sq. in. I Prof. Pike§ tested half brick flat¬ 
wise between sheets of pasteboard with the following results: St. 
Louis brick, 6,417 lbs. per sq. in. (the average of six trials); and 
pressed brick, 2,519 lbs. per sq. in.*(the average of thirteen sam¬ 
ples from ten localities). 

62. Size and Weight. In England the legal standard size for 
brick is 8| X 4f X 2f inches. In Scotland the average size is 
about 9^- X 4J X 3|- inches; in Germany, 9J X 4f X 2f inches ; in 
Austria, 11J X 5J x 2f inches; in Cuba, 11 X 5J X 2J inches; and 
in South America, 12f X 6£ X 2J inches. 

In the United States there is no legal standard, and the dimen¬ 
sions vary with the maker. In the Eastern States 8£ X 4 X 2J- 
inches is a common size for brick, of which 23 make a cubic foot; 
but in the West the dimensions are usually a little smaller. The 
National Brick-makers’ Association in 1887 and the National 

* Civil Engineering, pp. 366 and 769. 

t Van Nostrand’s Engineering Magazine, vol. xxxiv. p. 240. From abstracts of 
the Inst, of C. E. 

t Jour. Frank. Inst., vol. lxv. p. 333; also Trans. Am. Soc. of C. E., vol. ii. pp 
185-86. 

§ Jour. Assoc. Engineering Soc., vol. iv. pp. 366-67. 




SIZE, WEIGHT, AND COST. 


47 


Traders and Builders* Association in 1889 adopted 8| X 4 X 
inches as the standard size for common brick, and 8f X 4|- X 
for face brick. The price should vary with the size. If, reckoned 
according to cubic contents, brick 8x4x2 inches is worth $10 
per thousand, brick 8| x 4} x is worth $12.33 per thousand, 
and 8J X 4J- X 2J- is worth $15 per thousand. Further, where brick 
is laid by the thousand, small bricks are doubly expensive. Since 
bricks shrink in burning, in proportion to the temperature to which 
they are exposed, the amount differing with the different kinds of 
clays, it is impossible to have the size exactly uniform. Re-pressed 
and machine-moulded bricks are more nearly uniform in size than 
hand-moulded. 

The size of brick and the thickness of the mortar joint should 
be such that brick may be laid flat, edgewise, or set vertically, and 
still fit exactly. These proportions are seldom realized. 

Re-pressed brick weighs about 150 lbs. per cu. ft. ; common 
hard brick, 125 ; inferior, soft brick, 100. Common bricks will 
average about 4J lbs. each. 

63. Cost. Brick is sold by the thousand. At Chicago, in 1887., 
the “ best sewer** brick cost $9 ; common brick, from $6 to $7. 



CHAPTER III. 


LIME AND CEMENT. 

64. Classification. Considered as materials for use in the 
builder’s art, the products of calcination of limestone are classified 
as common lime, hydraulic lime, and. hydraulic cement. If the 
limestone is nearly pure carbonate of lime, the product is common 
lime, which will slake upon the addition of water, and mortar made 
of it will harden by absorbing carbonic acid from the air, but will 
not harden under water. If the limestone contains more impuri¬ 
ties, the product is hydraulic lime, which will slake upon the addi¬ 
tion of water, and mortar made of it will harden either in air or 
under water by the chemical action between the hydraulic lime and 
the water used in making the mortar. If the limestone contains 
still more impurities, the product is hydraulic cement, which will 
not slake upon the addition of water but must be reduced to a paste 
by grinding, and which will set either in air or under water by the 
chemical action between the cement and the water used in making 
the mortar. Common lime is sometimes called air-lime, because a 
paste or mortar made from it requires exposure to the air to enable 
it to “ set,” or harden. The hydraulic limes and cements are also 
called water-limes and water-cements, from their property of 
hardening under water. 

Common lime is used in making the mortar for most architect¬ 
ural masonry, and until recently it was generally employed in 
engineering masonry; but the opinion is rapidly gaining ground 
that only cement mortar should be employed in engineering struct¬ 
ures requiring great strength or subject to shock. On most first- 
class railroads hydraulic cement mortar is used in all masonry 
structures. This change in practice is largely due to the better 
appreciation of the superiority of hydraulic cement as a building 
material. Although it has been manufactured for about fifty 
years, the amount used was comparatively limited until within 
recent years. At present large quantities are imported from 

48 


ART. 1.] 


COMMON LIME. 


49 


Europe, and very much more is made in this country. Hydraulic 
lime is neither manufactured nor used in this country. 

The following discussion concerning common and hydraulic 
limes is given as preliminary to the study of hydraulic cements 
rather than because of the importance of these materials in engineer¬ 
ing constructi>n 


Art. 1. Common Lime. 

65. Descriition. The limestones which furnish the common 
lime are seldom, if ever, pure; but usually contain, besides the car¬ 
bonate of lime, from 3 to 10 per cent, of impurities,—such as silica, 
alumina, magnesia, oxide of manganese, and traces of the alkalies. 
Lime—variously designated as common lime, quicklime, or caustic 
lime—is a protoxide of calcium, and is produced when marble, or 
any other variety of pure or nearly pure carbonate of lime, is 
calcined with a heat of sufficient intensity and duration to expel 
the carbonic acid. It has a specific gravity of 2.3, is amorphous, 
highly caustic, has a great avidity for water, and when brought into 
contact with it will rapidly absorb nearly a quarter of its weight of 
that substance. This absorption is accompanied and followed by a 
great elevation of temperature, by the evolution of hot and slightly 
caustic vapor, by the bursting of the lime into pieces; and finally 
the lime is reduced to a powder, the volume of which is from two 
and a half to three and a half times the volume of the original lime 
—the increase of bulk being proportional to the purity of the lime¬ 
stone. In this condition the lime is said to be slaked, and is ready 
for use in making mortar. 

The paste of common lime is unctuous and impalpable to sight 
and touch; hence these limes are sometimes called fat or rich limes, 
as distinguished from others known as poor or meager limes. These 
latter usually contain more or less silica and a greater proportion of 
other impurities than the fat limes. In slaking they exhibit a more 
moderate elevation of temperature; evolve less vapor; are seldom 
reduced to an impalpable homogeneous powder; yield thin paste; 
and expand less. They are less valuable for mortar than the fat 
limes, but are extensively employed as fertilizers. When used for 
building purposes they should, if practicable, be reduced to powder 
by grinding, in order to remove all danger of subsequent slaking. 




50 


LIME AND CEMENT. 


[CHAP. III.. 


66. Testing. Good lime may be known by the following 
characteristics: 1. Freedom from cinders and clinkers, with not 
more than 10 per cent, of other impurities,—as silica, alumina, etc. 
2. Chiefly in hard lumps, with but little dust. 3. Slakes readily 
in water, forming a very fine smooth paste, without any residue. 
4. Dissolves in soft water, when this is added in sufficient quanti¬ 
ties. These simple tests can be readily applied to any sample of 
lime. 

67. Preserving. As lime abstracts water from the atmosphere 
and is thereby slaked, it soon crumbles into a fine powder, losing 
all those qualities which render it of value for mortar. On this 
account great care must be taken that the lime to be used is freshly 
burned, as may be known by its being in hard lumps rather than 
in powder. Lime is shipped either in bulk or in casks. If in bulk, 
it is impossible to preserve it for any considerable time; if in casks, 
it may be preserved for some time by storing in a dry place. 

Common lime, when mixed to a paste with water, may be kept 
for an indefinite time in that condition without deterioration, if 
protected from contact with the air so that it will not dry up. It 
is customary to keep the lime paste in casks, or in the -wide, shallow 
boxes in which it was slaked, or heaped up on the ground, covered 
over with the sand to be subsequently incorporated with it in mak¬ 
ing mortar. It is convenient for some purposes to keep the slaked 
lime on hand in a state of powder, which may be done in casks 
under cover, or in bulk in a room set apart for that purpose. The 
common limes contain impurities which prevent a thorough, 
uniform, and prompt slaking of the entire mass, and hence the 
necessity of slaking some days before the lime is to be used, to 
avoid all danger to the masonry by subsequent enlargement of 
volume and change of condition. 

A paste or mortar of common lime will not harden under water, 
nor in continuously damp places excluded from contact with the 
air. It will slowly harden in the air, from the surface toward the 
interior, by desiccation and the gradual absorption of carbonic-acid 
gas, by which process is formed a subcarbonate with an excess of 
hydrated base. 

68. Cost. Lime is sold by the barrel (about 230 pounds net), 
or by the bushel (75 pounds). At Chicago the average price, in 
1898, was from 55 to 60 cents per barrel. 


I 



ART. 2.] 


HYDRAULIC LIME. 


51 


Art. 2. Hydraulic Lime. 

69. Description. Hydraulic lime is like common lime in that 
it will slake, and differs from it in that it will harden under water. 
Hydraulic lime may be either argillaceous or siliceous. The former 
is derived from limestones containing from 10 to 20 per cent, of 
clay, homogeneously mixed with carbonate of lime as the principal 
ingredient; the latter from siliceous limestones containing from 12 
to 18 per cent, of silica. Small percentages of oxides of iron, car¬ 
bonates of magnesia, etc., are generally present. 

During the burning, the carbonic acid is expelled, and the silica 
and alumina entering into combination with a portion of the lime 
form both the silicate and the aluminate of lime, leaving in the 
burnt product an excess of quick or caustic lime, which induces 
slaking, and becomes hydrate of lime when brought into contact 
with water. The product owes its liydraulicity to the crystallizing 
energy of the aluminate and the silicate of lime. 

Hydraulic lime is slaked by sprinkling with just sufficient water 
to slake the free lime. The free lime has a greater avidity for the 
water than the hydraulic elements, and consequently the former 
absorbs the water, expands, and disintegrates the whole mass while 
the hydraulic ingredients are not affected. Hydraulic lime is 
usually slaked, screened, and packed in sacks or barrels before 
being sent to market. It may be kept without injury in this form 
as long as it is protected from moisture and air. 

No hydraulic lime is manufactured in the United States. It is 
manufactured in several localities in Europe, notably at Teil and 
Scilly, in France, from which places large quantities were formerly- 
brought to this country. 

Art. 3. Hydraulic Cement. 

70. Classification. Hydraulic cement may be divided accord¬ 
ing to the method of manufacture into three classes, viz.: Portland 
cement, natural cement, and pozzuolana. The first two differ from 
the third in that the ingredients of which the first two are composed 
must be roasted before they acquire the property of hardening under 
water, while the ingredients of the third need only to be pulverized 
and mixed with water to a paste. 



52 


LIME AND CEMENT. 


[CHAP. III. 


71. Portland. Portland cement is produced by calcining a 
mixture containing from 75 to 80 per cent, of carbonate of lime and 
20 to 23 per cent, of clay, at such a liigli temperature that the silica 
and alumina of the clay combines with the lime of the limestone. 
As the quantity of uncombined lime is not sufficient to cause the 
mass to slake to a powder upon the addition of water, the cement 
must be reduced to powder by grinding. 

To secure a complete chemical combination of the clay and the 
lime, it is necessary that the raw materials shall be reduced to a 
powder and be thoroughly mixed before burning, and also necessary 
that the calcination shall take place at a high temperature. These 
are the distinguishing characteristics of the manufacture of Portland 
cement. 

In a general way Portland cement differs from natural cement 
by being heavier, slower setting, and stronger. 

72. Portland cement derives its name from the resemblance 
which hardened mortar made of it bears to a stone found in the isle 
of Portland, off the south coast of England. Portland cement was 
made first in England about 1843, and in America about 1874. 

Until recent years nearly all the Portland cement used in this 
country was imported, but at present (1898) about one fifth of the 
•consumption is of domestic manufacture. The best American 
Portland is better than the best imported, and is sold equally cheap. 
In 1896 Portland cement was made at twenty-six places in the 
United States. Raw material suitable for the manufacture of Port¬ 
land cement exists in great abundance in nature, and with proper 
care a high-class Portland cement may be produced in almost any 
part of the country. 

In recent years the amount of cement used in this country has 
greatly increased, but the proportion of Portland used has increased 
at a much more rapid rate. In 1887 only about one fifth was 
Portland, while in 1897 one third was Portland. 

73. Natural Cement. Natural cement is produced by calcining 
;at a comparatively low temperature either a natural argillaceous 
limestone or a natural magnesian limestone without pulverization, 
nr the admixture of other materials. The stone is quarried, broken 
into pieces, and burned in a kiln. The burnt cement is then 
crushed into small fragments, ground, packed, and sent to market. 

In the process of manufacture natural cement is distinguished 



A LIT. 3.] 


HYDRAULIC CEMENT. 


53 


from Portland, in using a natural instead of an artificial mixture 
and in calcining at a lower temperature. As a product, natural 
cement is distinguished from Portland in weighing less, being less 
strong, and as a rule setting more quickly. 

In Europe in making this class of cement argillaceous limestone 
is generally used, and the product is called Roman cement. In the 
United States magnesian limestone is usually employed in making 
this cement; and formerly there was great diversity in the term 
used to designate the product, domestic, American, and natural 
being employed. In the early editions of this volume, the author 
called this class of cement Rosendale, from the place where it was 
first made in this country—Rosendale, Ulster Co., N. Y. The 
term natural is now quite generally used, and on the whole it seems 
the best. 

74. In 1896 natural cement was made in sixty-eight places in 
seventeen states in this country, and it may safely be assumed that 
there is no very large area in which a stone can not be found from 
which some grade of natural cement can be made. 

Nearly one half of the natural cement made in this country 
comes from Ulster Co., N. Y., and nearly half of the remainder 
comes from near Louisville, Kentucky. 

75. Pozztjolana. Pozzuolana is a term applied to a combina¬ 
tion of silica and alumina which, when mixed with common lime 
and made into mortar, has the property of hardening under water. 
There are several classes of materials possessing this property. 

Pozzuolana proper is a material of volcanic origin, and is the 
first substance known to possess the peculiar property of hydrau- 
licity. The discovery was made at Pozzuoli, near the base of 
Mount Vesuvius,—hence the name. Vitruvius and Pliny both 
mention that pozzuolana was extensively used by the Romans before 
their day; and Vitruvius gives a formula for its use in monolithic 
masonry, which with slight variations has been followed in Italy 
ever since. It is as follows: “ 12 parts pozzuolana, well pulverized; 
6 parts quartzose sand, well washed; and 9 parts rich lime, well 
slaked.” 

Trass is a volcanic earth closely resembling pozzuolana, and is 
employed substantially in the same way. It is found on the Rhine 
between Mayence and Cologne, and in various localities in Holland. 

Arenes is a species of ocherous sand containing so large a pro- 



54 


LIME AND CEMENT. 


[CHAP. III. 


portion of clay that it can be mixed into a paste with water without 
the addition of lime, and used in that state for common mortar. 
Mixed with rich lime it yields hydraulic mortar of considerable 
energy. 

Brick dust mixed with common lime produces a feebly hydraulic 

mortar. 

76. Slag Cement. Slag cement is by far the most important of 
the pozzuolana cements. It is the product obtained by mixing 
powdered slaked lime and finely pulverized blast-furnace slag. The 
amount of slag cement manufactured is very small as compared 
with Portland or natural cement, and apparently much more is 
manufactured in Europe than in America.' Probably most of the 
so-called pozzuolana cements are slag cements. It is claimed that 
slag cement mortar will not stain the stone laid with it. 

77. Weight. Cement is generally sold by the barrel, although 
not necessarily in a barrel. Imported cement is always sold in 
barrels, but American cement is sold in barrels, or in bags, or less 
frequently in bulk. 

Portland cement usually weighs 400 pounds per barrel gross, 
and 370 to 380 pounds net. A bag of Portland usually weighs 95 
pounds, of which four are counted a barrel. 

Natural cement made in or near Rosendale, N. Y., weighs 318 
pounds per barrel gross, and 300 net. Cement made in Akron, 
N. Y., Milwaukee, Wis., Utica, Ill., Louisville, Ky., weighs 285 
pounds per barrel gross, and 265 net. Cloth bags usually contain 
one third, and paper bags one fourth of a barrel. 

Slag cement weighs from 325 to 350 pounds net per barrel. 

78. Cost. The price of hydraulic cement has decreased greatly 
in recent years, owing chiefly to the development of the cement 
industry in this country. At present the competition among 
domestic manufacturers governs the price. In 1898 the prices in 
car-load lots were about as follows: 

Imported Portland cement at Atlantic ports $1.50 to $2 per 
barrel in wood, and at Chicago $2 to $2.50. American Portland at 
eastern mills is $1.50 to $1.75 in wood, and in the Mississippi valley 
$1.75 to $2. The price in paper bags is about 10 cents per barrel 
less than in wood, and about 15 cents per barrel cheaper in cloth 
bags than in wood—provided the cloth bags are returned to the 
mill, freight prepaid. 



ART. 4.] 


TESTS OF CEMENT. 


55 


Natural cement in the Rosendale (N. Y.) district costs f. o. b. 
mills 50 cents per barrel (300 pounds net) in bulk, 60 cents in 
paper, and 70 cents in wood. The price at the western mills in 
recent years was 50 cents per barrel (265 pounds net) in cloth (the 
sacks to be returned, freight prepaid), 55 cents in paper, and 60 
cents in wood. 

Slag cement is made in this country only at Chicago, where it 
sells at prices but little below those of similar grades of Portland 
ceipents. The imported pozzuolana sells substantially the same as 
similar grades of Portland. 

Art. 4. Tests of Cement. 

79. The value of a cement varies greatly with the chemical 
composition, the temperature of calcination, the fineness of grind¬ 
ing, etc.; and a slight variation in any one of these items may 
greatly affect the physical properties of the product. Unless the 
process of manufacture is conducted with the utmost care, two lots 
of cement of the same brand are liable to differ considerably in 
physical properties. Therefore the testing of cement to determine 
its fitness for the use proposed is a matter of very great importance. 
The properties of a cement which are examined to determine its 
constructive value are: (1) color, (2) thoroughness of burning, (3) 
activity, (4) soundness, (5) fineness, (6) strength. 

80. Color. The color of the cement powder indicates but 
little, since it is chiefly due to oxides of iron and manganese, which 
in no way affect the cementitious value; but for any given brand, 
variations in shade may indicate differences in the character of the 
rock or in the degree of burning. 

With Portland cement, gray or greenish gray is generally con¬ 
sidered best; bluish gray indicates a probable excess of lime, and 
brown an excess of clay. An undue proportion of under-burned 
material is generally iudicated by a yellowish shade, with a marked 
difference between the color of the hard-burned, unground particles 
retained by a fine sieve and the finer cement which passes through 
the sieve. 

Natural cements are usually brown, but vary from very light to 
very dark. 

Slag cement has a mauve tint—a delicate lilac. 




56 


LIME AND CEMENT. 


[CHAP. III. 


81. Thoroughness of Burning. The higher the temperature 
of burning the greater the weight of the clinker (the unground 
cement). Two methods have been employed in utilizing this prin¬ 
ciple as a test of the thoroughness of burning, viz.: (1) determine 
the weight of a unit of volume of the ground cement, and (2) 
determine the specific gravity of the cement. 

82. Weight. For any particular cement the weight varies with 
the temperature of burning, the degree of fineness in grinding, and 
the density of packing. Other things being the same, the harder- 
burned varieties are the heavier. The finer a cement is ground the 
more bulky it becomes, and consequently the less it weighs. Hence 
light weight may be caused by laudable fine grinding or by objec¬ 
tionable under-burning. 

The weight per unit of volume is usually determined by sifting 
the cement into a measure, and striking the top level with a straight¬ 
edge. In careful work the height of fall and the size of the meas¬ 
uring vessel are specified. The weight per cubic foot is neither 
exactly constant, nor can it be determined precisely; and is of very 
little service in determining the value of a cement. However, it is 
often specified as one of the requirements to be fulfilled. The fol¬ 
lowing values, determined by sifting the cement with a fall of three 
feet into a box having a capacity of one tenth of a cubic foot, may 
be taken as fair averages for ordinary cements. The difference in 
weight for any particular kind is mainly due to a difference in fine¬ 
ness : 


Portland 75 to 90 lbs. per cubic foot, or 94 to 112 lbs. per bushel. 

Natural 50 to 56 lbs. per cubic foot, or 62 to 70 lbs. per bushel. 

Specifications for the reception of cement frequently specify the 
net weight per barrel; but this is a specification for quantity and 
not quality. 

83. Specific Gravity. The determination of the specific gravity 
of a cement is the only real test of the thoroughness of burning. 
The specific gravity is determined by immersing a known weight 
of the cement in a liquid which will not act upon it (usually turpen¬ 
tine or benzine), and obtaining the volume of the liquid displaced. 
The specific gravity is equal to the weight of the cement (in 
grammes) divided by the displaced volume (in cubic centimetres). 

A variety of forms of apparatus for use in making this test are 



ART. 4.] 


TESTS OF CEMENT. 


57 


upon the market, but as several of the volumeters in ordinary use 
in chemical and physical laboratories are suitable for this purpose, 
it is unnecessary to describe any of them here. As a slight differ¬ 
ence in specific gravity is frequently accompanied by a considerable 
difference in the quality of the cement, great care is necessary in 
making the test. It is necessary that all the air-bubbles contained 
in the cement powder be eliminated, so that the volume obtained 
be that of the cement particles only. The cement should be passed 
through a sieve, say No. 80, to eliminate the lumps. The tempera¬ 
ture of the liquid should not be above 60° Fahr., and should not 
change during the test. A change of 1° C. in the turpentine 
between the readings of the volumeter will make a difference of 
0.08 in the resulting specific gravity. 

The specific gravity of Portland cement varies from 3.00 to 3.25, 
usually between 3.05 and 3.17. Natural cement varies from 2.75 to 
3.05, and is usually between 2.80 and 3.00. Slag cement has a 
specific gravity of 2.72 to 2.76. The specific gravity of cement 
decreases with age owing to the absorption of water and carbonic acid 
from the air. 

German authorities state that the specific gravity of fresh Port¬ 
land cement is between 3.12 and 3.25. English specifications re¬ 
quire 3.10 for fresh Portland and 3.07 for cement 3 months old. 
By the specifications of the Canadian Society of Civil Engineers 
the minimum for fresh Portland is 3.09. Many specifications fix 
3.00 or 3.05 for the lower limit. 

84. Activity. When cement powder is mixed with water to a 
plastic condition and allowed to stand, the cement chemically com¬ 
bines with the water and the entire mass gradually becomes firm 
and hard. This process of solidifying is called setting. Cements 
differ very wddely in their rate and manner of setting. Some 
occupy but a few minutes in the operation, while others require 
several hours. Some begin to set comparatively early and take 
considerable time to complete the process, while others stand con¬ 
siderable time without apparent change and then set very quickly. 

A knowledge of the activity of a cement is of importance both 
in testing and in using a cement, since its strength is seriously 
impaired if the mortar is disturbed after it has begun to set. 
Ordinarily the moderately slow-setting cements are preferable, since 
they need not be handled so rapidly and may be mixed in larger 





58 


LIME AND CEMENT. 


[CHAP. III. 


quantities; but in some cases it is necessary to use a rapid-setting 
cement, as for example when an inflow of water is to be prevented. 

To determine the rate of setting, points have been arbitrarily 
fixed where the set is said to begin and to end. It is very difficult 
to determine these points with exactness, particularly the latter; 
but an exact determination is not necessary to judge of the fitness 
of a cement for a particular use. For this purpose it is ordinarily 
sufficient to say that a mortar has begun to set when it has lost its 
plasticity, i.e ., when its form cannot be altered without producing 
a fracture; and that it has set hard when it will resist a slight 
pressure of the thumb-nail. Cements will increase in hardness long 
after they can not be indented with the thumb-nail. 

For an accurate determination of rate of set two standards are 
in use, viz.: Gillmore’s and the German. 

85. Gillmore's Test. Mix the cement with water to a stiff 
plastic mortar (see §§ 103-4), and make a cake or pat 2 or 3 inches 
in diameter and about | inch thick. The mortar is said to have 
begun to set when it will just support a wire y^-inch in diameter 
weighing ^ pound, and to have “ set hard ” when it will bear a -fa- 
inch wire weighing 1 pound. A loaded wire used for this purpose 
is frequently called a Yicat needle, after Yicat, its inventor. The 
interval between the time of adding the water and the time when 
the light wire is just supported is the time of beginning to set, and 
the interval between the time the light wire is supported and the 
time when the heavy one is just supported is the time of setting. 

86. German Test.* “ A slow-setting cement (one setting in not 
less than two hours) shall be mixed three minutes, and a quick¬ 
setting cement (one setting in less than two hours) one minute, with 
water to a stiff paste. The consistency of the cement paste for this 
cake shall be such that, when wrought with a trowel on the plate, 
the paste will only begin to run towards the edge of the same after 
the paste has been repeatedly jarred. As a rule, 27 to 30 per cent, 
of water will suffice to give the necessary consistency to a Portland 
cement paste, f 

“For the exact determination of the time of beginning to set, 
and for determining the time of setting, a standard needle 300 

* Specifications of the Prussian Minister of Public Works, July 28, 1887. 
t Apparently this mortar is more moist than the “ plastic mortar ” ordinarily 
employed in this country (see §§ 10J-4). 





ART. 4.] 


TESTS OF CEMENT. 


59 


grammes (11 oz.) in weight and 1 square millimetre (0.0006 square 
inch) in cross-section is used. A metal ring 4 centimetres (1.575 
inches) in height and 8 centimetres (3.15 inches) clear diameter 
(inside) is placed on a glass plate, filled with cement paste of the 
above consistency, and brought under the needle.* The moment 
at which the needle is no longer capable of completely penetrating 
the cement cake is considered the beginning of the time of setting. 
The time elapsing between this and the moment when the standard 
needle no longer leaves an appreciable impression on the hardened 
cake is considered the time of setting.” 

To facilitate the making of this test, an apparatus is provided 
which consists of a light rod freely sliding through an arm; and 
carrying in its lower end the penetrating needle. The amount of 
penetration is read by an index moving over a graduated scale. 

87. Elements Affecting Rate of Set. The amount of water 
employed is important. For data as to the amount of water to be 
used, see §§ 103-4. The less the water, the more rapid the set. 

It is usually specified that the temperature of the water and air 
shall be from 60° to 65° F. The higher the temperature, the more 
rapid the set. To prevent the surface of the test specimen from 
hardening by drying, it is specified that the pat shall be immersed 
in water at 60° to 65° F. The setting under water is much slower 
than in air even though the air be saturated with moisture and be 
at the same temperature as the water, due to the mechanical action 
of the water. 

Other things being the same, the finer the cement is ground the 
quicker it sets. 

Cements usually become slower setting with age, particularly if 
exposed to the air—Portlands usually but slightly. 

The standard tests for activity are usually made on neat cement 
on account of the interference of the sand grains with the descent 
of the needle. The rate of setting of neat mortar gives but little 
indication of what the action may be with sand. Sand increases 
the time of setting—but very differently for different cements. 
With some cements a mortar composed of one part cement to three 
parts sand will require twice as long to set as a neat' mortar, while 
with other cements the time will be eight or ten times as long. 

* For an illustration of the apparatus see Trans. Amer. Soc. of C. E., vol. xxx. 

p. 11. 






60 


LIME AND CEMENT. 


[CHAP. III. 


Sulphate of lime (plaster of Paris) greatly influences the rate of 
setting of Portland cements. The addition of 1 or 2 per cent, is 
sufficient to change the time of setting from a few minutes to several 
hours. Cement which has been made slow-setting by the addition of 
sulphate of lime, usually becomes quick-setting again after exposure 
to the air; cement which has not had its time of setting changed 
by the addition of sulphate of lime, usually becomes slower setting 
with age and may finally lose the power of setting. Cement which 
has become slow-setting by the addition of sulphate of lime will 
become quick-setting if mixed with a solution of carbonate of 
soda. 

A weak solution of chloride of lime usually causes the cement 
to set more slowly; while a strong solution usually accelerates the 
rate of setting. 

88. Time of Set. A few of the quickest natural cements when 
tested neat with the minimum of water will begin to set in 5 to 10 
minutes, and set hard in 15 to 20 minutes; while the majority will 
begin to set in 20 to 30 minutes and will set hard in 40 to 60 
minutes; and a few of the slowest will not begin to set under 60 
minutes. 

The quickest of the Portlands will begin to set in 20 to 40 min¬ 
utes; but the majority will not begin to set under 2 or 3 hours, 
and will not set hard under 6 or 8 hours. The 1887 standard 
German specifications reject a Portland cement which begins to 
set in less than 30 minutes or which sets hard in less than 
3 hours. 

89. Soundness. Soundness refers to me ability of a cement to 
retain its strength and form unimpaired for an indefinite period. 
Soundness is a most important element; since if a cement ultimately 
loses its strength it is worthless, and if it finally expands it becomes 
a destructive agent. A cement may be unsound because of the 
presence in it of some active elements which cause the mortar to 
expand or contract in setting, or the unsoundness may be due to 
exterior agencies which act upon the ingredients of the cement. 
Most unsound cements fail by swelling and cracking under the 
action of expansives; but sometimes the mortar fails by a gradual 
softening of the mass without material change of form. The ex¬ 
pansive action is usually due to free lime or free magnesia in the 
cement, but may be caused by sulphur compounds. The principal 



ART. 4.] 


TESTS OF CEMENT. 


61 


exterior agencies acting upon a cement are air, sea-water, and 
extremes of heat and cold. 

The presence of small quantities of free lime in the cement is a. 
frequent cause of unsoundness. The lime slakes, and causes the 
mortar to swell and crack—and perhaps finally disintegrate. The 
degree of heat employed in the burning, and the fineness, modify 
the effect of the free lime. Lime burned at a high heat slakes 
more slowly than when burned at a low temperature, and is there¬ 
fore more likely to be injurious. Finely ground lime slakes more 
quickly than coarsely ground, and hence with fine cement the lime 
may slake before the cement has set, and therefore do no harm. 
The lime in finely ground cements will air-slake sooner than that in 
coarsely ground. 

Free magnesia in cement acts very much like free lime. The 
action of the magnesia is much slower than that of lime, and hence 
its presence is a more serious defect, since it is less likely to be 
detected before the cement is used. The effect of magnesia in 
cement is not thoroughly understood, but seems to vary with the 
composition of the cement, the degree of burning, and the amount 
of water used in mixing. It was formerly held that or 2 per 
cent, of magnesia in Portland cement was dangerous; but it is now 
known that 5 per cent, is not injurious, while 8 per cent, may pro¬ 
duce expansion. Since many of the natural cements are made of 
magnesium limestone, they contain much more magnesia than 
Portland cements; but chemists are not agreed as to the manner in 
which the different constituents are combined, and consequently are 
not agreed either as to the amount or effect of free magnesia in such 
a cement. Fortunately, it is not necessary to resort to a chemical 
analysis to determine the amount of lime or magnesia present, for 
a cement which successfully stands the ordinary test for soundness. 
(§ 92) for 7, or at most 28 days, may be used with reasonable con¬ 
fidence. 

The effect of lime and magnesia seem3 to be more serious, 
in water than in air, and greater in sea-water than in fresh 
water. 

90. The action of sulphur in a cement is extremely variable, 
depending upon the state in which it may exist and upon the 
nature of the cement. Sulphur may occur naturally in the cement 
or may be added in the form of sulphate of lime (plaster of Paris) 



I 


'62 LIME AND CEMENT. [CHAP. III. 

to retard the time of set (§ 87). Under certain conditions the 
sulphur may form sulphides, which on exposure to the air oxidize 
and form sulphates and cause the mortar to decrease in strength. 
Many, if not all, of the slag cements contain an excess of sulphides, 
and are therefore unfit for use in the air, particularly a very dry 
atmosphere, although under water they may give satisfactory results 
and compare favorably with Portland cement. 

91. Tests of Soundness. Several methods of testing soundness 
have been recommended. Of those mentioned below, the first two 
are called cold tests, since the mortar is tested at ordinary tempera¬ 
tures; and the others accelerated or hot tests. 

92. The Pat Test. The ordinary method of testing soundness 
Is to make small cakes or pats of neat mortar 3 or 4 inches in 
diameter, about half an inch thick and having thin edges, upon a 
sheet of glass, and examine from day to day, for 28 days (if 
possible), to see if they show any cracks or signs of distortion. 
The amount of water used in mixing (see § 104) within reason¬ 
able limits seems to have no material effect on the result. The 
German standard specifications require the cake to be kept 24 
hours in a closed box or under a damp cloth, and then stored in 
water. The French, to make sure that the pats do not get dry 
before immersion, recommend that the cakes be immersed immedi¬ 
ately after mixing without waiting for the mortar to set. Some 
really sound natural cements will disintegrate if immersed before 
setting has begun. 

The first evidence of bad quality is the loosening of the pat from 
the glass, which generally takes place, if at all, within one or two 
days. Good cement will remain firmly attached to the glass for two 
weeks at least. The cracks due to expansion occur usually at the 
edges of the pat, and radiate from the center. These cracks should 
not be confused with irregular hair-like shrinkage cracks, which 
appear over the entire surface when the pats are made too wet and 
-dry out too much while setting. 

93. A cement high in sulphides, as for example one made of 
blast-furnace slag, will successfully pass the above, the usual, test 
for soundness; and still the mortar when exposed in the air will 
show a marked decrease in strength and perhaps finally dis¬ 
integrate. The presence of an excess of sulphides may be sus¬ 
pected in any cement made from blast-furnace slag. A slag 



ART. 4.] 


TESTS OF CEMENT. 


63 


cement is indicated by a mauve or delicate lilac tint of the dry 
powder. 

Therefore, in making the pat test, it is wise to expose a pat in 
the air as well as one under water. Any sulphides in the cement 
will be revealed by brown or yellowish blotches on the pat exposed 
in air, and also by a greenish color of the interior of the pat exposed 
under water. The pat in air is not as good a test of expansives as. 
the pat under water, owing to a possible deficiency of water and to 
greater shrinkage cracks. 

If there are any considerable indications of sulphides, before 
accepting the cement a chemical analysis should be made to deter¬ 
mine the sulphur and the probable ultimate action of the cement. 
Any cement containing sulphides in appreciable quantities is at 
least doubtful and should probably be rejected. Slag cements 
usually contain 1 to 1.5 per cent, of sulphides. 

Another excellent method of examining for the presence of sul¬ 
phides is, in making the test for tensile strength (§§ 99-111^), to 
store part of the briquettes in air and part in water. Any material 
difference in strength between the two lots is sufficient ground for 
rejecting the cement for use in a dry place. Of course due con¬ 
sideration should be given to the possible effect of evaporation of 
water from the briquettes stored in air. 

94. Expansion Test. Various experimenters test the soundness 
of cement by measuring the expansion of a bar of cement mortar. 
The French Commission recommend the measurement of the expan¬ 
sion of a bar 32 inches long by \ inch square, or the measurement 
of the increase of circumference of a cylinder. The German 
standard tests require the measurement of the increase in length of 
a prism 4 inches long by 2 inches square. The apparatus for 
making these tests can be had in the market. The tests require 
very delicate manipulation to secure reliable results. 

95. Accelerated Tests. The ordinary tests extending over a 
reasonable period, sometimes fail to detect unsoundness; and many 
efforts have been made to utilize heat to accelerate the action, with 
a view of determining from the effect of heat during a short time 
what would be the action in a longer period under normal condi¬ 
tions. Some of these tests have been fairly successful, but none 
have been extensively employed. It is difficult to interpret the 
tests, as the results vary with the per cent, of lime, magnesia, sul- 




LIME AND CEMENT. 


[CHAP. III. 


fi4 


phates, etc., present, and with their proportions relative to each 
other and to the whole. There is a great diversity as to the value 
of accelerated tests. Many natural cements which go all to pieces 
in the accelerated tests, particularly the boiling test, still stand 
well in actual service. This is a strong argument against drawing 
adverse conclusions from accelerated tests when applied to Portland 
cement. 

The warm-water test , proposed by Mr. Faija,* a British 
authority, is made with a covered vessel partly full of water 
maintained at a temperature of 100° to 115° F., in the upper 
part of which the pat is placed until set. When the pat is 
set, it is placed in the water for 24 hours. If the cement remains 
firmly attached to the glass and shows no cracks, it is very probably 
sound. 

The hot-water test , proposed by Mr. Maclay,f an American 
authority, is substantially like Faija’s test above, except that 
Maclay recommends 195° to 200° F. 

The toiling test , suggested by Professor Tetmajer, the Swiss 
authority, consists in placing the mortar in cold water immediately 
after mixing, then gradually raising the temperature to boiling 
after about an hour, and boiling for three hours. The test 
specimen consists of a small ball of such a consistency that when 
flattened to half its diameter it neither cracks nor runs at the 
edges. 

The kiln tests consist of exposing a small cake of cement 
mortar, after it has set, to a temperature of 110° to 120° C. 
(166° to 248° F.) in a drying oven until all the water is driven off. 
If no edge cracks appear, the cement is considered of constant 
volume. 

The flame test is made by placing a ball of the cement paste, 
about 2 inches in diameter, on a wire gauge and applying the 
flame of a Bunsen burner gradually until at the end of an hour the 
temperature is about 90° C. (194° F.). The heat is then in¬ 
creased until the lower part of the ball becomes red-hot. The 
appearance of cracks probably indicates the presence of an expansive 
element. 


* Trans. Am. Soc. of C. E., vol. xvii. p. 223; vol. xxx. p. 57. 
t Trans. Am. Soc. of C. E., vol. xxvii. p. 412. 





ART. 4.] 


TESTS OF CEMENT. 


65 


The chloride-of-lime test is to mix the paste for the cakes with 
■a solution of 40 grammes of calcium chloride per liter of water, 
allow to set, immerse in the same solution for 24 hours, and then 
examine for checking and softening. The chloride of lime accel¬ 
erates the hydration of the free lime. The chloride in the solution 
used in mixing causes the slaking before setting of only so much of 
the free lime as is not objectionable in the cement. The chloride 
of calcium has no effect upon free magnesia. 

96. Fineness. The question of fineness is wholly a matter of 
■economy. Cement until ground is a mass of partially vitrified 
clinker, which is not affected by water, and which has no setting 
power. It is only after it is ground that the addition of water 
induces crystallization. Consequently the coarse particles in a 
cement have no setting power whatever, and may for practical 
purposes be considered as so much sand and essentially an adul¬ 
terant. 

There is another reason why cement should be well ground. A 
mortar or concrete being composed of a certain quantity of inert 
material bound together by cement, it is evident that to secure a 
strong mortar or concrete it is essential that each piece of aggregate 
shall be entirely surrounded by the cementing material, so that no 
two pieces are in actual contact. Obviously, then, the finer a 
cement the greater surface will a given weight cover, and the more 
economv will there be in its use. 

Fine cement can be produced by the manufacturers in three 
ways: 1, by supplying the mill with comparatively soft, under-burnt 
rock, which is easily reduced to powder; 2, by more thorough 
grinding; or 3, by bolting through a sieve and returning the 
unground particles to the mill. The first process produces an in¬ 
ferior quality of cement, while the second and third add to the cost 
of manufacture. 

It is possible to reduce a cement to an impalpable powder, but 
the proper degree of fineness is reached when it becomes cheaper to 
use more cement in proportion to the aggregate than to pay the 
extra cost of additional grinding. 

97. Measuring Fineness. The degree of fineness is determined 
by weighing the per cent, which will not pass through sieves of a 
specified number of meshes per square inch. In the past, three 
sieves have been used for this purpose, viz., sieves having 50, 75, 



66 


LIME AND CEMENT. 


[CHAP. Ill* 


and 100 meshes per linear inch, or 2,500, 5,625, and 10,000 meshes 
per square inch respectively. These sieves are usually referred to 
by the number of meshes per linear inch, the first being known as 
No. 50, the second as No. 75, and the third as No. 100. In each 
case the diameter of the mesh is about equal to that of the wire. 
The per cent, left on the coarser sieves has no special significance, 
and hence the use of more than one sieve has been almost aban¬ 
doned. More recently in this country a No. 120 sieve (14,400 
meshes per square inch) has been employed, and sometimes a 
No. 200. On the continent of Europe the sieve generally used has 
70 meshes jier linear centimetre, corresponding to 175 meshes per 
linear inch (30,625 per square inch). 

98. Data on Fineness. Nearly all Portland cements are so 
ground as not to leave more than 20 per cent, on a No. 100 sieve, 
and many of them will not leave more than 10 per cent, on a 
No. 100 sieve or more than 20 per cent, on a No. 200 sieve; and 
some manufacturers claim less than 10 per cent, on a No. 200 sieve. 
As a rule, American Portlands are finer ground than German, and 
German finer than English. 

Most of the natural cements are usually ground so as to give 
not more than 20 per cent, on the No. 100 sieve, and many of them 
will not leave more than 10 per cent, on the No. 100 sieve, and a 
few will leave only 10 per cent, on the No. 200 sieve. 

A common specification is that not more than 10 per cent, shall 
be left on a No. 50 sieve. Such a test simply prevents the adultera¬ 
tion of the cement with very coarse particles, but does not insure 
any considerable proportion of impalpable powder (approximately 
that which will pass a No. 200 sieve), which alone gives value to 
the cement.* 

Sinse the natural cement is not so hard burned as the Portland, 
there is more impalpable powder in proportion to the per cent, left 
on the test sieve than with the Portland; and consequently a severe 
test for fineness is not as important for natural cement as for 


* There has recently been introduced an article called sand-cement, which is 
made by mixing cement and silica sand and grinding the mixture. The grind¬ 
ing of the mixture greatly increases the fineness of tho cement. A mixture of 
1 part cement and 3 parts silica sand when reground will carry nearly as much 
sand as the original pure cement, which shows the striking effect of the very 
fine grinding of the cement. 





ART. 4.] 


TESTS OF CEMENT. 


67 


Portland. Farther, since nataral cement is much cheaper than 
Portland, it is more economical to use more cement than to 
require extra fineness. Again, since natural cement is weaker, 
it is not ordinarily used with as large a proportion of sand as 
Portland, and hence fineness is not as important with natural as with 
Portland. 

For various specifications for fineness, see Art. 5, pages 78 d- 
78 h, particularly Tables 10c and 10/ pages 78/, 7 Sg. 

99. Tensile Strength. The strength of cement mortar is 
usually determined by submitting a specimen having a cross section 
of 1 square inch to a tensile stress. The reason for adopting tensile 
tests instead of compressive is the greater ease of making the former 
and the less variation in the results. Mortar is eight to ten times 
as strong in compression as in tension. 

The accurate determination of the tensile strength of cement is 
a much less simple process than at first appears. Many things, 
apparently of minor importance, exert such a marked influence upon, 
the results that it is only by the greatest care that trustworthy tests 
can be made. The variations in the results of different experienced 
operators working by the same method and upon the same material 
are frequently very large. In one particular test case,* the lowest 
of nine results was but 30 per cent, of the highest, the remainder 
being evenly distributed between the two extremes. Similar varia¬ 
tions are not at all unusual. The variation is chiefly due to differ¬ 
ences in making the test specimen. Unfortunately, there is at 
present no detailed standard method of procedure in making the 
tests, and consequently all that can be done is to observe with the 
most conscientious care the rules that have been formulated, and 
draw the specifications in accordance with the personal equation of 
the one to make the tests. 

100. Neat vs. Sand Tests. It is very common to test neat-cement 
mortar, but there are two serious objections to this practice. First,, 
most neat cements decrease in tensile strength after a time. This 
decrease seems to be due to a change in the molecular structure of 
the cement, the crystals growing larger with increase of age, thus 
producing a crowding which results in a decrease of the tensile 
strength. This decrease is most marked with high-grade Portlands 


* Engineering News, vol. xxxv. pp. 150-51. 






68 


LIME AND CEMENT. 


[CHAP. III. 


which attain their strength rapidly, and usually occurs between 
three months and a year. A second objection to neat tests is that 
coarsely-ground cements show greater strength than finely-ground 
cements, although the latter mixed with the usual proportion of 
sand will give the greater strength. 

On the other hand, more skill is required to secure uniform 
results with sand than with neat cement. 

101. The Sand. The quality of the sand employed is of great 
importance, for sands looking alike and sifted through the same 
sieve give results varying 30 to 40 per cent. 

The standard sand employed in the official German tests is a 
natural quartz sand obtained at Freienwalde on the Oder, passing 
a sieve of 60 meshes per square centimetre (20 per linear inch) and 
caught upon a sieve of 120 meshes per square centimetre (28 per 
linear inch). The standard “sand” recommended by the Com¬ 
mittee of the American Society of Civil Engineers is crushed quartz, 
used in the manufacture of sand-paper, which passes a No. 20 sieve 
(wire No. 28 Stubs’s gauge) and is caught on a No. 30 sieve (wire 
No. 30 Stubs’s gauge), the grains being from 0.03 to 0.02 inch in 
diameter. 

The crushed quartz consists of sharp, glossy splinters, while the 
standard German sand is composed of nearly spherical grains having 
ja rough surface like ground glass. The quartz contains about 50 
per cent, of voids, while the German standard sand contains only 
about 40 (see Table lOy, page 79?*.) The crushed quartz will give 
less strength than standard sand. Ordinarily common building sand 
will give a higher strength than standard sand, since usually the 
former consists of grains having a greater variety of sizes, and con¬ 
sequently there are fewer voids to be filled by the cement (see Table 
10y, page 79 i.) 

102. The Amount of Water. The amount of water necessarv 
to make the strongest mortar varies with each cement. It is com¬ 
monly expressed in per cents, by weight, although in part at least 
it depends upon volume. The variation in the amount of water 
required depends upon the degree of fineness, the specific gravity, 
the weight per unit of volume, and the chemical composition. If 
the cement is coarsely ground, the voids are less, and consequently 
the volume of water required is less. If the specific gravity of one 
cement is greater than that of another, equal volumes of cement 



ART. 4.] 


TESTS OF CEMENT. 


69 


will require different volumes of water. The chemical composition 
has the greatest influence upon the amount of water necessary. 
Part of the water is required to combine chemically with the cement, 
and part acts physically in reducing the cement to a plastic mass; 
and the portion required for each of these effects differs with differ¬ 
ent cements. The dryness and porosity of the sand may also 
appreciably affect the quantity of water required. The finer the 
sand, the greater the amount of water required. Again, the same 
consistency may be arrived at in two ways—by using a small quan¬ 
tity of water and working thoroughly, or by using a larger 
quantity and working less. (For instructions concerning mixing, 
see § 106). 

Attempts have been made to establish a standard consistency, 
but there is no constant relation between the consistency and the 
maximum strength. With one cement a particular consistency may 
give maximum strength, while with another cement a different con¬ 
sistency may be required to develop the greatest strength. The 
relationship between consistency and strength will vary also with 
the details of the experiment. In reporting the results of tests the 
quantity of water employed should be stated. 

There are two distinct standards of consistency for the mortar 
employed in testing cements,—the plastic and the dry. 

103. Plastic Mortar. This grade of mortar is that com¬ 
monly employed in the United States and England, and is fre¬ 
quently used in France.* There are two methods of identifying 
this degree of consistency, viz.: the Tetmajer method and the 
Boulogne method. The Tetmajer method requires more water 
than the Boulogne method—for Portland this excess is about 3 
per cent, of the weight of the cement, and for natural about 5 
per cent. 

The Tetmajer method is much used on the continent of Europe. 

, It is as follows: The plasticity shall be such that a rod 0.4 of an 
inch in diameter and weighing 0.66 pounds will penetrate 1.25 
inches into a box 3 inches in diameter and 1.57 inches deep, filled 
with the mortar.f 

The Boulogne method is frequently used in France. It is as 
* See foot note, page 71. 

t For an illustration of the apparatus, see Trans. Amer. Soc. of C. E., vol. xxx. 
J>. 11- 








70 


LIME AND CEMENT. 


[CHAP. III. 


follows: * “ The quantity of water is ascertained by a preliminary 
experiment. It is recommended to commence with a rather smaller 
quantity of water than may be ultimately required, and then to 
make fresh mixings with a slight additional quantity of water. 
The mortar is to be vigorously worked for five minutes with a trowel 
on a marble slab to bring it to the required consistency, after which 
the four following tests are to be applied to determine whether the 
proportion of water is correct: 1. The consistency of the mortar 
should not change if it be gauged for an additional period of three 
minutes after the initial five minutes. 2. A small quantity of the 
mortar dropped from the trowel upon the marble slab from a height 
of about 0.50 metres (20 inches) should leave the trowel clean, and 
retain its form approximately without cracking. 3. A small quan¬ 
tity of the mortar worked gently in the hands should be easily 
moulded into a ball, on the surface of which water should appear. 
When this ball is dropped from a height of 0.50 metres (20 inches), 
it should retain a rounded shape without cracking. 4. If a slightly 
smaller quantity of water be used, the mortar should be crumbly, 
and crack when dropped upon the slab. On the other hand, the 
addition of a further quantity of water—1 to 2 per cent, of the 
weight of the cement—would soften the mortar, rendering it more 
sticky, and preventing it from retaining its form when allowed to 
fall upon the slab. ” 

104. With any particular cement the exact amount of water to 
produce the above degree of plasticity can be determined only by 
trial, but as a rule the quantity required by the Boulogne method 
will be about as follows: 

For neat cement: Portland, 23 to 25 per cent.; natural, from 
30 to 40, usually from 32 to 3G per cent. 

For 1 part cement to 1 part sand: Portland cement, 13 to 15 
per cent, of the total weight of cement and sand; natural, 17 to 
20, usually 18 to 19 per cent. 

For 1 part cement to 2 parts sand: Portland, 12 to 13 per cent, 
of the total weight of the sand and cement; natural, 12 to 16, 
usually 13 to 15 per cent. 

For 1 part cement to 3 parts sand: Portland, 11 to 12 per cent. 


* From abstracts of Inst, of C. E. 





ART. 4.] 


TESTS OF CEMENT. 


71 


of the total weight of the sand and cement; natural, 12 to 13 per 
cent. 

105. Dry Mortar. This grade of mortar is employed in the 
German and French * governmental tests of tensile strength. The 
rules for the identification of this degree of consistency are not very 
specific. “ Dry mortars ” are usually described as being “ as damp 
as moist earth.” 

The German government does not recognize tensile tests of neat 
cement mortar; but for 1 to 3 sand mortars specifies that the weight 
of water used for Portland cement shall be equal to 10 per cent, of 
the total weight of the sand and cement. 

The French Commission gives a rule \ for 1 to 2, 1 to 3, and 
1 to 5 mortars, with either Portland or natural cement, which is 
equivalent to the following formula: 


w — § WIl + ^5, 

in which w — the weight, in grammes, of water required for 

1,000 grammes of the sand and cement; 

W = the weight, in grammes, of water required to re¬ 
duce 1,000 grammes of neat cement to plastic 
mortar (see § 104); 

R = the ratio of the weight of the cement to the weight 
of the sand and cement. 

For a 1 to 3 mortar the preceding formula gives 8.5 per cent., 
which seems to show that the French standard requires less water 
than the German. 

The cement laboratory of the city of Philadelphia employs the 
above formula, but uses 60 for the constant instead of 45. For a 
1 to 3 mortar, the Philadelphia formula gives 10 per cent., which 
agrees with the German standard. 

106. Mixing the Mortar. The sand and cement should be 
thoroughly mixed dry, and the water required to reduce the mass 
to the proper consistency should be added all at once. The mixing 


* The French Commission recommends dry mortar for tensile tests only; and 
also recommends that, after an international agreement to that effect, plastic 
mortars he employed for all tests to the exclusion of dry mortars. 

f Carter and Gieseler’s Conclusions adopted hy the French Commission in 
reference to Tests of Cements, p. 21. 





72 


LIME AND CEMENT. 


[CHAP. Ill* 


should be prompt and thorough. The mass should not be simply 
turned, but the mortar should be rubbed against the top of the 
slate or glass mixing-table with a trowel, or in a mortar with a 
pestle. Insufficient working greatly decreases the strength of the 
mortar—frequently one half. The inexperienced operator is very 
liable to use too much water and too little labor. With a slow- 
setting cement a kilogramme of the dry materials should be strongly 
and rapidly rubbed for not less than 5 minutes, when the consist¬ 
ency should be such that it will not be changed by an additional 
mixing for 3 minutes. 

Usually the mortar is mixed with a trowel on a stone slab; but 
when many batches are required, there is a decided advantage in 
mixing the mortar with a hoe in a short Y-shaped trough on the 
floor. Various machines have been devised with which to mix the 
mortar. The jig mixer* is an apparatus in which the materials are 
placed in a covered cup, and shaken rapidly up and down. The 
Faija mixer f consists of a cylindrical pan in which a mixer 

formed of four blades revolves. The 

ri —m -~r- 1 latter seems to give the better result, 

but neither are used to any considerable 
extent. 

107. The Form of Briquette. The 

briquette recommended by the Committee 
of the American Society of Civil En¬ 
gineers, Fig. 2, is the form ordinarily 
used in this country and in England. 
The form generally employed in con¬ 
tinental Europe is somewhat similar to 
the above, except that the section is 5 
square centimetres (0.8 square inch) and 
the reduction to produce the minimum 
section is by very much more abrupt 
curves.]; The latter form gives only 70 
to 80 per cent, as much strength as the former. 



Fig. 


* For illustrated description, see Trans. Amer. Soc. of C. E., vol. xxv. p. 300-1. 
f For British form, see Trans. Am. Soc. of C. E., vol. xvii. p. 223; and for the 
American form, see catalogue of Itiehle Bros. Testing Machine Co., Philadelphia. 

J For an elaborate discussion of the best form of briquette, see Johnson’s 
Materials of Construction, p. 432-38. 
















ART. 4.] 


TESTS OF CEMENT. 


73 


The moulds are made of brass and are single or multiple, the 
latter being preferred where a great number of briquettes is required. 
The moulds are in two parts, to facilitate removal from the 
briquette without breaking it. 

108. Moulding the Briquette. In moulding the briquette there 
are two general methods employed, corresponding to the two stand¬ 
ard consistencies of the mortar. 

109. Plastic Mortar. The rules of this section (109) apply to 
hand-moulding . 

The Committee of the American Society of Civil Engineers’ 
recommendations are as follows: “ The moulds while being charged 
should be laid directly on glass, slate, or some non-absorbing 
material. The mortar should be firmly pressed into the moulds . 
with a trowel, without ramming, and struck off level. The mould¬ 
ing must be completed before incipient setting begins. As soon as 
the briquettes are hard enough to bear it, they should be taken 
from the moulds and kept covered with a damp cloth until they 
are immersed.” 

The French Commission recommends the following method:* 

“ The moulds are placed upon a plate of marble or polished metal 
which has been well cleaned and rubbed with an oiled cloth. Six 
moulds are filled from each gauging if the cement be slow-setting, 
and four if it be quick-setting. Sufficient material is at once placed 
in each mould to more than fill it. The mortar is pressed into the 
mould with the fingers so as to leave no voids, and the side of the 
mould tapped several times with the trowel to assist in disengaging 
the bubbles of air. The excess of mortar is then removed by slid¬ 
ing a knife-blade over the top of the mould so as to produce no 
compression upon the mortar. The briquettes are removed from 
the mould when sufficiently firm, and are allowed to remain for 24 
hours upon the plate in a moist atmosphere, protected from currents 
of air or the direct rays of the sun, and at a nearly constant tem¬ 
perature of 15° to 18° C. (59° to 64.4° F.).” 

110. Various machines have been devised for moulding bri¬ 
quettes of plastic mortar, but none are used to any considerable 
extent, f 


* Carter and Gieseler’s Conclusions adopted by the French Commission in 
reference to Tests of Cements, p. 23. 

f For an illustrated description of Russell’s lever machine, see Trans. Amer. Soc. 





74 


LIME AND CEMENT. 


[CHAP. III. 


In Canada, and to some extent in England, the briquettes are 
moulded by applying a pressure of 20 pounds per square inch on the 
surface of the briquette.* * Some advocate a pressure of 1,000 to 
1,500 pounds upon the upper face of the briquette.f 

111. Dry Mortar. The rules of this section (111) are for hand- 
moulding. 

The German standard rules are: \ “ On a metal or thick glass 
plate five sheets of blotting-paper soaked in water are laid, and on 
these are placed five moulds wetted with water. 250 grammes 
(8.75 oz.) of cement and 750 grammes (2G.25 oz.) of standard sand 
are weighed, and thoroughly mixed dry in a vessel. Then 100 
cubic centimetres (100 grammes or 35 oz.) of fresh water are added, 
and the whole mass thoroughly mixed for five minutes. With the 
mortar so obtained, the moulds are at once filled, with one filling, 
so high as to be rounded on top, the mortar being well pressed in. 
By means of an iron trowel 5 to 8 centimetres (1.96 inches to 3.14 
inches) wide, 35 centimetres (13.79 inches) long, and weighing 
about 250 grammes (8.75 oz.), the projecting mortar is pounded, 
first gently and from the side, then harder into the moulds, until 
the mortar grows elastic and water flushes to the surface. A 
pounding of at least one minute is absolutely essential. An addi¬ 
tional filling and pounding in of the mortar is not admissible, since 
the test pieces of the same cement should have the same densities 
at the different testing stations. The mass projecting over the 
mould is now cut off with a knife, and the surface smoothed. The 
mould is carefully taken off and the test piece placed in a box lined 
with zinc, which is to be provided with a cover, to prevent a non- 
uniform drying of the test pieces at different temperatures. 
Twenty-four hours after being made, the test pieces are placed 
under water, and care must be taken that they remain under water 
during the whole period of hardening.” 

The French Commission recommend the following for sand 


of C. E., vol. xxvii. p. 441; ditto of Jamieson’s lever machine, see The Transit 
(Iowa State University), Decembor, 1889. or Engineering News, vol. xxv. p. 138, or 
Trans. Amer. Soc. of C. E., vol. xxv. p. 302. 

* Trans. Canadian Soc. of C. E., vol. ix. p. 56, “ Final Report of the Committee on 
a Standard Method of Testing Cements.” 
f Spalding’s Hydraulic Cement, p. 135. 

J Engineering News, vol. xvi. p. 316. 




I 


ART. 4.] TESTS OF CEMENT. 75 

mortars: “ Sufficient mortar is gauged at once to make six 
briquettes, requiring 250 grammes of cement and 750 grammes of 
normal sand. The mould is placed upon a metal plate, and upon 
top of it is fitted a guide haying the same section as the mould and 
a height of 125 millimetres (5 inches). 180 grammes of the mortar 
are introduced and roughly distributed in the mould and guide with 
a rod. By means of a metallic pestle weighing 1 kilogramme, and 
having a base of the form of the briquette but of slightly less 
dimensions, the mortar is pounded softly at first, then stronger and 
stronger until a little water escapes under the bottom of the mould. 
The pestle and guide are then removed and the mortar cut off level 
with the top of the mould.” 

111a. The Bohme hammer apparatus is much used, particularly 
in Germany. It consists of an arrangement by which the mortar 
is compacted in the mould by a succession of blows of a hammer 
weighing 2 kilogrammes (2.2 pounds) upon a plunger sliding in a 
guide placed upon top of the mould. The machine is arranged to 
lock after striking 150 blows. A high degree of density is thus 
produced, and more regular results are obtained than by hand. 
The apparatus is slow.* 

The Tetmajer apparatus! is similar in character to the Bohme 
hammer. “ It consists of an iron rod carrying a weight upon its 
lower end, which is raised through a given height and dropped upon 
the mortar in the mould. The ram weighs 3 kilogrammes. This 
machine is used in the Zurich laboratory, and Prof. Tetmajer regu¬ 
lates the number of blows by requiring a certain amount of work 
to be done upon a unit volume of mortar,—0.3 kilogrammetre of 
work per gramme of dry material of which the mortar is composed. 
This apparatus is subject to the same limitations in practice as the 
Bohme hammer, in being very slow in use and somewhat expensive 
in first cost.” 

Ill A Storing the Briquettes. It is usual to store the briquettes 
under a damp cloth or in a moist chamber for 24 hours, and then 
immerse in water at a temperature of 60° to 65° F. For one-day 
tests, the briquettes are removed from the moulds and immersed as 


* For an illustrated description, see Engineering News, vol. xvii. p. 200; Trans. 
Amer. Soc. of C. E., vol. xxx. p. 24. 

f French Commission’s Report, vol. i. p. 287. 





76 


LIME AND CEMENT. 


[CHAP. III. 


soon as they have begun to set. The volume of the water should 
be at least four times the volume of the immersed briquettes, and 
the water should be renewed every seven days. 

The briquettes should be labeled or numbered to preserve their 
identity. Neat-cement briquettes may be stamped with steel dies,, 
as may also sand briquettes, provided a thin layer of neat cement is 
spread over one end in which to stamp the number. 

111c. Age when Tested. Since in many cases it is impracticable 
to extend the tests over a longer time, it has become customary to 
break the briquettes at one and seven days. This practice, together 
with a demand for high tensile strength, has led manufacturers to 
increase the proportion of lime in their cements to the highest 
possible limit, which brings them near the danger-line of unsound¬ 
ness. A high strength at 1 or 7 days is usually followed by a 
decrease in strength at 28 days. Steadily increasing strength at 
long periods is better proof of good quality than high results during 
the first few days. The German standard test recognizes only 
breaks at 28 days. The French standard permits, for slow-setting 
cements, tests at 7 and 28 days, and 3 and 6 months, and 1, 2, 
etc., years; and for rapid-setting cements, from 3 to 24 hours for 
neat mortar and 24 hours for sand mortars. In all cases the time 
is counted from the instant of adding the water when mixing the 
briquette. The briquettes should be tested as soon as taken from 
the water. 

11 If?. The Testing Machine. There are two types in common 
use. In one the weight is applied by a stream of shot, which runs 
from a reservoir into a pail suspended at the end of the steelyard 
arm; when the briquette breaks the arm falls, automatically cutting 
off the How of shot. In the other type, a heavy weight is slowly 
drawn along a graduated beam by a cord wound on a wheel turned 
by the operator. The first is made by Fairbanks Scale Co., and the 
second by Riehle Bros., and also by Tinius Olsen, both of Phila¬ 
delphia. 

Fig. 3 represents a cement-testing machine which can be 
made by an ordinary mechanic at an expense of only a few 
dollars. Athough it does not have the conveniences and is not 
as accurate as the more elaborate machines, it is valuable where 
the quantity of work will not warrant a more expensive one, and 
in many cases is amply sufficient. It was devised by F. W. Bruce 




ART. 4.] 


TESTS OF CEMENT. 


n 


for use at Fort Marion, St. Augustine, Fla., and reported to the 
Engineering News (vol. v. pp. 194-96) by Lieutenant W. M. Black, 
U. S. A. 

The machine consists essentially of a counterpoised wooden lever 
10 feet long, working on a horizontal pin between two broad 
uprights 20 inches from one end. Along the top of the long arm 
runs a grooved wheel carrying a weight. The distances from the 
fulcrum in feet and inches are marked on the surface of the lever. 
The clamp for holding the briquette for tensile tests is suspended 
from the short arm, 18 inches from the fulcrum. Pressure for 
shearing and compressive stresses is communicated through a loose 
upright, set under the long arm at any desired distance (generally 
6 or 12 inches) from the fulcrum. The lower clip for tensile strains 
is fastened to the bed-plate. On this plate the cube to be crushed 



W, fixed weight. W\ rolling weight. W", counterpoise. B\ block for shearing. B, 
block for crushing. C, tensile strain clips. 

rests between blocks of wood, and to it is fastened an upright with 
a square mortise at the proper height for blocks to be sheared. The 
rail on which the wheel runs is a piece of light T-iron fastened on 
top of the lever. The pin is iron and the pin-holes are reinforced by 
iron washers. The clamps are wood, and are fastened by clevis, 
joints to the lever arm and bed-plate respectively. When great 
stresses are desired, extra weights are hung on the end of the long 
arm. Pressures of 3,000 pounds have been developed with this 
machine. 

For detailed drawings of a more elaborate home-made cement¬ 
testing machine, see Proceedings Engineers’ Club of Philadelphia, 
vol. v. p. 194, or Engineermg Neius , vol. xv. p. 310. 

1 He. The Clips. The most important part of the testing 
machine are the clips, by means of which the stress is applied 
to the briquette. 1. The form must be such as to grasp the 





















78 


LIME AND CEMENT. 


[CHAP. III. 


briquette on four symmetrical surfaces. 2. The surface of con¬ 
tact must be large enough to prevent the 
briquette from being crushed between the 
points of contact. 3. The clip must turn 
without appreciable friction when under 
stress. 4. The clip must not spread ap¬ 
preciably while subjected to the maximum 
load. 

The form of clip recommended by the 
Committee of the American Society of 
Civil Engineers is shown in Fig. 4. This 
-k form does not offer sufficient bearing sur¬ 
face, and the briquette is frequently crushed 
at the point of contact. The difficulty is 
remedied somewhat by the use of rubber- 
tipped clips. 

Whatever the form of the machine or 
clips, great care should be taken to center 
the briquette in the machine. 

Ill/. The Speed. The rate at which 
the stress is applied makes a material 
difference in the strength. The following 
data are given by H. Faija,* an English 
authority, as showing the effect of a variation in the speed of 
applying the stress: 





r 

J 


L 


Fig. 4. 


Rate. 

100 pounds in 120 seconds 


Tensile Strength. 
. 400 pounds. 


100 “ “ 60 . 415 “ 

100 “ “ 30 “ 430 

100 “ “ 15 “ 450 “ 

100 “ “ 1 “ 493 “ 


The French and German standard specifications require 660 
pounds per minute. The American Society of Civil Engineers 
recommends 400 pounds per minute for strong mixtures, and half 
this speed for weak mixtures. The Canadian Society of Civil 
Engineers recommends 200 pounds per minute. 

lll$ f . Data on Tensile Strength. Owing to the great variation 


* Trans. Amer. Soc. of C. E., vol. xvii. p. 227. 























ART. 4.] 


TESTS OF CEMENT. 


7 8a 


in the manner of making the tests, it is not possible to give any very 
valuable data on the strength that good cement should show. In 
1885 a Committee of the American Society of Civil Engineers 
recommended the values given in Table 10 below. At least the 
minimum values there given are required in ordinary specifications, 
and the maximum values are sometimes employed. Many of the 


TABLE 10. 

Tensile Strength of Cement Mortars. 



Average Tensile Strength 
in Pounds per Square Inch. 

Age of Mortar when Tested. 






Portland. 

Natural. 

Clear Cement. 

Min. 

Max. 

Min. 

Max. 

1 day—1 hour, or until set, in air, the remainder 





of the time in water. 

100 

140 

40 

80 

1 week—1 day in air, the remainder of the time 





in water. 

250 

550 

60 

100 

4 weeks—1 day in air, the remainder of the time 





in water. 

1 year—1 day in air, the remainder of the time 
in water. 

350 

450 

700 

800 

100 

150 

300 

400 

1 Part Cement to 1 Part Sand. 





1 week—1 day in air, the remainder of the time 





in water. 



30 

50 

4 weeks—1 day in air, the remainder of the time 



in water. 



50 

80 

1 year—1 day in air, the remainder of the time 

in wn.tp.r . 



200 

300 

1 Part Cement to 3 Parts Sand. 



1 week—1 day in air, the remainder of the time 





in water . 

80 

125 



4 weeks—1 day in air, the remainder of the time 



in water. 

100 

200 



1 year—1 day in air, the remainder of the time 
in water. 



200 

350 





better cements commonly give results above the maximum values 
in the table. Natural cement, neat plastic mortar, will generally 
show 50 to 75 pounds per square inch in 7 days, and 100 to 200 in 




























LIME AND CEMENT. 


[CHAP. III. 


7 8 b 


28 days. Good Portland cement, neat plastic mortar, will show 
100 to 200 pounds per square inch in one day, 400 to 600 in 
7 days, and 600 to 800 in 28 days. With 3 parts sand, Portland 
cement, plastic mortar, will give at least 100 pounds per square 
inch in 7 days, and 200 in 28 days. Of course the strength varies 
greatly with the method of testing. In consulting authorities on 
this subject, it should be borne in mind that the strength of cement, 
particularly Portland, has greatly increased in the past 10 years. 
The specifications should be drawn to correspond with the personal 
equation of the one who is to test the cement. 

For various specifications for tensile strength, see Art. 5, pages 
78c-7S/i, particularly Tables 10c and 10 d, pages 78/, 78^. 

For additional data on the strength of mortars composed of 
different proportions of cement and sand, see Fig. 5, page 91. 

Ill h. Equating the Results. It not infrequently occurs that 
several samples of cement are submitted, and it is required to 
determine which is the most economical. One may be high-priced 
•and have great strength; another may show great strength neat 


TABLE 10a. 

Relative Economy of Cements Tested Neat at 7 Days. 


Cements. 

Fineness. 

Tensile Strength. 

Cheapness. 

Relative 

Economy. 

Per cent. Passing 
No. 100 Sieve. 

% 

Relative. 

* 

Pounds per 

Square Inch. 

Relative. 

Cost per Barrel. 

Relative. 

Product of Rela¬ 
tive Fineness, 
Relative Strength, 
and Relative 

Cost. 

a 

a 

P3 

A 

90.0 

98.1 

628 

81.5 

$2.30 

100.0 

79.95 

2 

B 

88.0 

95.9 

771 

100.0 

2.34 

98.3 

94.26 

1 

C 

88.7 

96.6 

477 

61.9 

2.40 

95.8 

57.28 

4 

D 

91.8 

100.0 

391 

50.7 

2.45 

93.8 

47.55 

5 

E 

81.5 

88.8 

660 

85.6 

2.47 

93.1 

70.79 

3 


and be coarsely ground. If the cement is tested neat, then 
■strength, fineness, and cost should be considered; but if the cement 




































ART. 5. J 


SPECIFICATIONS FOR CEMENT. 


?8c 


as tested with the proportion of sand usually employed in practice, 
then only strength and cost need to be considered. 

Table 10# (page 78$) shows the method of deducing the relative 
economy when the cement is tested neat; and Table 10& shows the 


TABLE 106. 

Relative Economy of Cements Tested with Sand at 7 Days. 


Cements. 

Tensile Strength 

1 C. TO 3 s. 

Cheapness. 

Relative Economy. 

Pounds per 
Square 
Inch. 

Relative. 

Cost per 
Barrel. 

Relative. 

Product of 
Relative 
Strength 
and Relative 

Cost. 

Rank. 

A 

168 

95.4 

$2.30 

100.0 

95.40 

o 

B 

176 

100.0 

2.34 

98.3 

98.30 

1 

c 

166 

94.3 

2.40 

95.8 

90.33 

3 

D 

135 

76.7 

2.45 

93.8 

71.94 

4 

E 

135 

76.7 

2.47 

93.1 

71.40 

5 


method when the cement is tested with sand. The data are from 
actual practice, and the cements are the same in both tables. 
Eesults similar to the above could be deduced for any other 
age; the circumstances under which the cement is to be used 
should determine the age for which the comparison should be 
made. 

The above method of equating the results gives the advantage 
to a cement which gains its strength rapidly and which is liable to 
he unsound. Therefore this method should be used with discretion, 
particularly with short-time tests. 


Art. 5. Specifications for Cement. 

lilt. Cement is so variable in quality and intrinsic value that 
no considerable quantity should be accepted without testing it to 
see that it conforms to a specified standard. A careful study of 
Art. 4, preceding, will enable any one to prepare such specifications 
as will suit the special requirements, and also give the instructions 






























LIME AND CEMENT. 


[CHAP. HI. 


7 

necessary for applying the tests. A few specifications will be given 
to serve as guides in preparing others. 

SPECIFICATIONS FOR QUALITY. 

Ill j. German Portland. The following are the most im¬ 
portant paragraphs from the standard specifications of the German 
government as given in the ofiicial circular issued by the Minister 
of Public Works of Prussia under date of July 28, 1887 :* 

“ Time of Setting. According to the purpose for which it is intended, 
quick or slow-setting Portland cement may be demanded. Slow-setting cements 
are those that set in about two hours.” The test is made as described in 
§ 86 . 

“ Constancy of Volume. The volume of Portland cement should remain 
constant. The decisive test of this should be that a cake of cement, made on a 
glass plate, protected from sudden drying aud placed under water after 24 
hours, should show, even after long submersion, no signs of crumbling or of 
cracking at the edges.” For method of making the test, see § 92. 

“ Fineness of Grinding. Portland cement must be ground so fine that no 
more than 10 per cent, of a sample shall pass through a sieve of 900 meshes per 
square centimetre (5,800 per square inch). The thickness of the wires of the 
sieve to be one-half the width of the meshes.” Notice that a sieve having 900 
meshes per square centimetre (5,800 per sq. in.) is the standard, although 
sieves of 5,000 meshes per square centimetre (32,000 per sq. in.) are frequently 
used. 

“ 1'ests of Strength. The binding strength of Portland cement is to be 
determined by testing a mixture of cement and sand. The test is to be con¬ 
ducted for tensile and compressive strength according to a uniform method, 
aud is to be performed upon test specimens of like form, like cross section, and 
with like apparatus. It is recommended, besides, to determine the strength of 
neat cement. The tests for tension are to be made upon briquettes of 5 sq. 
cm. (0.78 sq. in.) cross section at the place of rupture, the tests for compression 
upon cubes of 50 sq. cm. (7.8 sq. in.) area.” 

"Tensile and Compressive Strength. Slow-setting Portland cement, when 
mixed with standard sand in the proportion of 1 part of cement to 3 of sand, 
by weight, 28 days after being mixed—one day in air and 27 in water—must 
possess a tensile strength of not less than 16 kilog. per square centimetre (225 
lbs. per square inch), and a maximum compressive strength of 160 kilog. per 
square centimetre (2,250 lbs. persq. in.). Quick-setting cements generally show 
a lower strength after 28 days than that given above. The time of setting 
must, therefore, be given when stating figures relative to strength.” The test is 
made as described in the second paragraph of §111 or the first paragraph of 
§ 111a. 


* Translation from Trans. Amer. Soc. of C. E., vol. xxx. pp. 10-21. 







ART. 5.J 


SPECIFICATIONS FOR CEMENT. 


78e 


111 Tc. English Portland. Iii Great Britain there are no 
official specifications, but the following proposed * by Mr. Henry 
Faija are much used: 

“ Fineness to be such that the cement will all pass through a sieve having 
625 holes (25 2 ) to the square inch, and leave only 10 per cent, residue when 
sifted through a sieve having 2,500 holes (50 2 ) to the square inch. 

“ Expansion or Contraction. A pat made and submitted to moist heat and 
warm water at a temperature of 100° to 115° F., shall show no sign of expan¬ 
sion or contraction (blowing) in twenty-four hours. 

“ Tensile Strength. Briquettes of slow-setting Portland, which have been 
gauged, treated, and tested in the prescribed manner, to carry an average ten¬ 
sile strain, without fracture, of at least 176 lbs. per sq. in. at the expiration of 
3 days from gauging; and those tested at the expiration of 7 days, to show an 
increase of at least 50 per cent, over the strength of those at 3 days, but to 
carry a minimum of 350 lbs. per sq. in. 

“For quick-setting Portland, at least 176 lb3. per sq. in. at 3 days, and an 
increase at 7 days of 20 to 25 per cent., but a minimum of 400 lbs. per sq. in. 
Very high tensile strengths at early dates generally indicate a cement verging: 
on an unsound one.” 

111Z. French Portland. The following are the requirements 
of the Services Mari times des Fonts et Chaussees,f and are fre¬ 
quently employed in France: 

“ Density. A liter measure is loosely filled with cement, previously 
screened through a sieve of 180 meshes to the linear inch, and weighed. This 
test is used for comparison of different lots of the same cement, the weight of 
1 liter of which must exceed a certain figure determined for the cement in 
question. No general requirement as to density is made.” 

“ Chemical Composition. Cement containing more than 1 per cent, of sul¬ 
phuric anhydride (=1.7 per cent, sulphate of lime) is rejected, while that con¬ 
taining more than 4 per cent, of oxide of iron is declared suspicious. Cement 
containing less than 44 parts of silica and alumina to 100 of lime is also con¬ 
sidered suspicious.” 

Time of Setting. The test for time of setting is made as described in § 86 
(page 58). “ Cement which begins to set in less than 30 minutes or sets com¬ 

pletely in less than 3 hours is refused.” 

“ Constancy of Volume. Pats on glass are immersed in sea-water kept 
at a temperature of 59° to 65° F., and examined for cracking or change of 
form.” 

“ Tensile Strength. The amount of water to be employed is determined as 


* Trans. Amer. Soc. of C. E., vol. xvii. p. 225; vol. xxx. (1893) p. 60. 
f Candlot’s “Ciments and Chaux Hydraulics,” Paris, 1891, pp. 150-61. 






78/ 


LIME AND CEMENT. 


[CHAP. III. 


in third paragraph of § 103 (page 69). The briquettes are moulded as de¬ 
scribed in in the third paragraph of § 109, page 73. 

“ For neat cement, the tensile strength at 7 days must be at least 20 kilog. 
per sq. cm. (284 lbs. per sq. in.); at 28 days, 35 kilog. per sq. cm. (497 lbs. 
per sq. in.); at 12 weeks, 45 kilog. per sq. cm. (639 lbs. per sq. in.). The 
tensile strength at 28 days must exceed that at 7 days by at least 5 kilog. per 
sq. cm. (71 lbs. per sq. in.). The tensile strength at 12 weeks must be greater 
than that at 28 days unless the latter shall be at least 55 kilog. per sq. cm. 
(781 lbs. per sq. in.). 

“ For 3 parts crushed quartz to 1 part cement, with 12 per cent, water 
[moulded as described in the third paragraph of §111], the tensile strength 
must be at 7 days at least 8 kilog. per sq. cm. (114 lbs. per sq. in.); at 28 days 
at least 15 kilog. per sq. cm. (213 lbs. per sq. in.); and at 12 weeks, 18 kilog. 
per sq. cm. (256 lbs. per sq. in.). The strength at 12 weeks must in all cases 
be greater than that at 28 days.” 

111m. American Practice. Tables 10c and 10 d give the average 
requirements for fineness and tensile strength of Portland and 
natural cements, for various classes of work in the United States. 
These values may be regarded as representative of the average 
American practice: 


TABLE 10c. 

American Requirements for Fineness and Strength of Portland 

Cement. 


Cfi 

a 

n 

3 

p 

$5 

w 

o 

55 

H 

C3 

H 

Average American Practice 
as Represented by 

Per cent. 
Passing 
Sieve. 
No. 

fc 

W 


50 

100 

1 

38 U. S. A. Engineers. 

95 

84 

2 

10 Cities. 

97 

89 

3 

6 Railways. 

95 

80 

4 

6 Bridges. 

97 

88 

5 

3 Aqueducts. 


80 

6 

81 Specifications. 

96 

85 


Tensile Strength, Lbs. per Sq. In. 


Neat Cement. 


Mortar. 


1 to 2. 


1 to 3. 


Age when Tested, Days. 


l 

7 

28 

ry 

( 

28 

7 

28 

131 

402 

547 

150 

200 

119 

189 

161 

388 

534 

145 

200 

132 

197 

115 

319 

483 

123 

175 

108 

150 

119 

347 

487 

142 

250 

132 

200 

110 

333 

400 

125 

200 

132 

225 

134 

384 

528 

146 

216 

118 

189 











































ART. 5.] 


SPECIFICATIONS FOR CEMENT. 


7 % 


TABLE 10 d. 

American Requirements for Fineness and Strength of Natural 

Cement. 


£ 

Ed 

03 

a 

E> 

£ 

Ed 

U 

fc 

03 

03 

Ed 

Ob 

Ed 

« 


I 


Average American Practice as 
Represented by 


Per cent. 
Passing 
Sieve. 
No. 


Tensile Strength. 
Lbs. per Sq. In. 


Neat Cement. 


1 to 2 
Mortar. 


Age when Tested. Days. 


50 


100 


1 



1 

2 

3 

4 


24 U. S. A. Engineers 

10 Cities. 

4 Railways. 

2 Bridges. . 


91 

93 

95 

95 


72 

81 


38 

70 

65 

55 


102 

134 

105 

87 


164 

237 

162 

185 


34 
40 
47 

35 


77 


80 

70 


5 

6 


3 Aqueducts, 


51 Specifications, 


92 


79 


60 

63 


117 

109 


200 50 

178 40 


75 

77 


11 In. Philadelphia: Natural and Portland. The follow¬ 
ing is an abstract of the specifications used in 1897 by the Depart¬ 
ment of Public Works of the City of Philadelphia. These 
specifications are inserted as showing the extreme of American 
practice in the high degree of fineness and great strength required. 
Compare these results with those in Tables 10c and 10 d. The 
Philadelphia specifications are not included in these tables. 

NATURAL CEMENT. 

“ Specific Gravity. The specific gravity shall not be less than 2.7. 

“ Fineness. The residue shall not leave more than 2 per cent on a No. 50 
sieve, nor 15 on a No. 100 sieve, nor 35 on a No. 200 sieve, the sieves having 
2,400,10,200, and 35,700 meshes per square inch and the diameter of the wire 
being 0.0090, 0.0045, and 0.0020 of an inch respectively. 

“ Constancy of Volume. Pats of neat cement one half inch thick with 
thin edges, immersed in water after hard set, shall show no signs of checking 
or disintegration. 

“ Time of Setting. It shall begin to set in not less than 10 minutes, and set 
hard in less than 30 minutes. 

“ Tensile Strength. The tensile strength of dry mortar [see last paragraph 
of § 105] shall not be less than in the accompanying table: 





































78h 


LIME AND CEMENT. 


[CHAP. III. 


Age when Tested. 


24 hours (in water after set hard). 

7 days (1 day in air, G days in water).. 
28 days (1 day in air, 27 days in water) 


Tensile Strength. 
Pounds per Square Inch. 


Neat. 


1 Cement to 
2 Quartz. 


100 

200 

300 


125 

200 


PORTLAND CEMENT. 

“ Specific Gravity. The specific gravity shall not be less than 3.0. 

“ Fineness. The residue shall not be less than 1 per cent, on a No. 50 sieve, 
10 on a No. 100 sieve, and 30 on a No. 200 sieve. 

“ Constancy of Volume. Same as for natural cement above. 

“ Time of Setting. The cement shall not develop initial set in less than 30 
minutes. 

“ Tensile Strength. The tensile strength of dry mortar [see last paragragh 
of § 105] shall not be less than in the accompanying table : 


Age when Tested. 

Tensile Strength. 

Pounds per Square Inch. 

Neat. 

1 Cement to 

2 Quartz. 

24 hours (in water after hard set). 

• 175 


7 days (1 day in air, 6 days in water). 

500 

170 

28 days (1 day in air, 27 days in water). 

600 

240 


SPECIFICATIONS FOR DELIVERY AND STORAGE. 

lllo. The preceding specifications prescribe the quality of the 
cement; and the following refer to the quantity, the sampling, and 
the storage. The tests under the former are made in the laboratory, 
those under the latter on the work. 

Package. The cement shall be delivered in strong barrels* lined with 


* It is customary to specify that the cement, particularly Portland, shall be 
delivered in barrels. The only reason for shipping in barrels is that the cement is 
better protected from the weather in barrels than in bags. The arguments in 




































ART. 5.] 


SPECIFICATIONS FOR CEMENT. 


78 i 


paper so as to be reasonably protected from the air and dampness. Each 
package shall be labeled with the brand, the manufacturer’s name, and the 
gross weight. 

Weight. The net weight of a barrel of cement shall be understood to be 
375 pounds of Portland, and 300 pounds of Eastern natural or 265 pounds of 
Western natural [see § 77, page 54]; and bags shall contain an aliquot part of 
a barrel. A variation of 2 per cent, is allowable in the weight of individual 
packages. Any broken barrel or torn bag may be rejected or accepted at half 
its original weight,—at the option of the Inspector. 

Time of Delivery. The inspection and tests will occupy at least ten * * days, 
and the Contractor shall submit the cement for sampling at least ten * days 
before desiring to use it. The Inspector shall be promptly notified upon the 
receipt of each shipment. 

Sampling. The cement from which to test the quality shall be selected by 
taking, from the interior of each of six f well-distributed barrels or bags in 
each car-load, sufficient cement to make from five to ten briquettes. These 
sixf portions, after being thrown together and thoroughly [mixed, will be 
assumed to represent the average of the whole car-load. 

Storage. All cement when delivered shall be fully protected from the 
weather ; and shall not be placed upon the ground without proper blocking 
under it. Accepted cement may be re-inspected at any time ; and if found 
to be damaged, it shall be rejected. Any cement damaged by water to such 
an extent as to show upon the outside of the barrel will be rejected. 

Inspection Marks. Cement which has been accepted may be so labeled by 
the Inspector ; and the Contractor shall preserve these labels from deface¬ 
ment and shall prevent their imitation. Rejected cement shall be so marke4 ; 
and tile Contractor shall promptly remove such cement. 

Basis for Rejecting. Each shipment of cement shall be tested for quantity 
and quality. If the average weight of the barrels or bags tested is less than 
the weight specified, a corresponding deduction shall be made in the price ; 
and if ten per cent, fails to conform to the requirements for quality, the entire 


favor of shipping in bags are: 1. The cost is less, since the cost of the barrel is 
eliminated. 2. The cement is more easily handled, since the weight of a unit is 
less. 3. In cloth bags the cement improves by seasoning, i.e., the contact with 
the air hydrates any free lime due to improper chemical combination or imperfect 
calcination. 4. The practice of shipping in barrels is only a survival from the time 
when the best cement was of European manufacture, which of necessity was 
shipped in barrels because of the excessive moisture in the holds of vessels. 5. In 
Europe Portland cement is usually shipped in cotton-duck bags. 

* For important w T ork this time is usually made thirty days. 

f This is the number specified by the Pennsylvania Railroad, a road noted for 
careful and thorough work. It is frequently specified that ten samples shall be 
taken; and in important workjwhere a single barrel of poor cement may materially 
affect the strength of the work, it is sometimes specified that each and every 
barrel shall be tested. 




78/ 


LIME AND CEMENT. 


[CHAP. III. 


shipment may be rejected. The failure of a shipment to meet the specifica¬ 
tions for quality may prohibit further use of that brand on the work. 

Barrels containing a large proportion of lumps shall be rejected. 

Refusal to Test. The Engineer reserves the right to refuse to test any 
brand which in his judgment is unsuitable for the work.* A barrel or bag 
which is not plainly labeled with the brand and maker’s name shall not be 
tested, and shall be immediately removed. 


* This provision is sometimes inserted to avoid the trouble and delay of testing 
any brand which the Engineer is reasonably certain is unfit for the work owing to 
its general reputation for poor quality or lack of uniformity. 




CHAPTER IIIa. 


SAND, GRAVEL, AND BROKEN STONE. 

112. Sand is used in making mortar; and gravel, or sand and 
broken stone, in making concrete. The qualities of the sand and 
broken stone have an important effect upon the strength and cost 
of the mortar and the concrete. The effect of the variation in these 
materials is generally overlooked, even though the cement is subject 
to rigid specifications. 

Art. 1. Sand. 

113. Sand is mixed with lime or cement to reduce the cost of 
the mortar; and is added to lime also to prevent the cracking which 
would occur if lime were used alone. Any material may be used to 
dilute the mortar, provided it has no effect upon the durability of 
the cementing material and is not itself liable to decay. Pulverized 
stone, powdered brick, slag, or coal cinders may be used ; but 
natural sand is by far the most common, although fine crushed 
stone, or “stone screenings,” are sometimes employed and are in 
some respects better than natural sand. - 

In testing cement a standard natural sand Qr crushed quartz is 
employed; but in the execution of actual work usually local natural 
sand must be employed for economic reasons. Before commencing 
any considerable work, all available natural sands and possible sub¬ 
stitutes should be examined to determine their values for use in 
mortar. 

114. Requisites for Good Sand. To be suitable for use in 

mortar, the sand should be sharp, clean, and coarse; and’the grains 
should be composed of durable minerals, and the size of the grains 
should be such as to give a minimum of voids, i.e., interstices 
between the grains. 

The usual specifications are simply: “ The sand shall be sharp, 
clean, and coarse.” 

114a. Durability. As a rule ocean and lake sands are more 

79 a 


79 b 


SAND. 


[CHAP. Illtf. 


durable than glacial sands. The latter are rock meal ground in the 
geological mill, and usually consist of silica with a considerable ad¬ 
mixture of mica, hornblende, feldspar, carbonate of lime, etc. The 
silica is hard and durable; but the mica, hornblende, feldspar, and 
carbonate of lime are soft and friable, and are easily decomposed 
by the gases of the atmosphere and the acids of rain-water. The 
lake and ocean sands are older geologically ; and therefore are 
usually nearly pure quartz, since the action of the elements has ' 
eliminated the softer and more easily decomposed constituents. 
Some ocean sands are nearly pure carbonate of lime, which is soft 
and friable, and are therefore entirely unfit for use in mortar. 
These are known as calcareous sands. 

The glacial sands frequently contain so large a proportion of 
soft and easily decomposed constituents as to render them unfit for 
use in exposed work, as for example in cement sidewalks. Instead 
of constructing exposed work with poor drift sand, it is better either 
to ship natural silica sand a considerable distance or to secure 
crushed quartz. Crushed granite is frequently used instead of sand 
in cement sidewalk construction; but granite frequently contains 
mica, hornblende, and feldspar which render it unsuitable for this 
kind of work. 

However, as a rule the physical condition of the sand is of more 
importance than its chemical composition. 

114 b. Sharpness. Sharp sand, i.e., sand with angular grains, 
is preferred to that with rounded grains because (1) the angular 
grains are rougher and therefore the cement will adhere better; and 
(2) the angular grains offer greater resistance to moving one on the 
other under compression. On the other hand, the sharper the sand 
the greater the proportion of the interstices between the grains 
(compare line 4 of Table 10#, page 79 1 , with the preceding lines of 
the table); and consequently the greater the amount of cement 
required to produce a given strength or density. But a high 
degree of sharpness is more important than a small per cent, of 
voids. 

The sharpness of sand can be determined approximately by 
rubbing a few grains in the hand, or by crushing it near the ear 
and noting if a grating sound is produced; but an examination 
through a small lens is better. Sharp sand is often difficult to 
obtain, and the requirement that “ the sand shall be sharp” is 
practically a dead letter in most specifications. 






/ 


ART. 1.] CLEANNESS. 790 

114c. Cleanness. Clean sand is necessary for the strongest 
mortar, since an envelop of loam or organic matter about the sand 
grains will prevent the adherence of the cement. The cleanness of 
sand may be judged by pressing it together in the hand while it is 
damp; if the sand sticks together when the pressure is removed, it 
is entirely unfit for mortar purposes. The cleanness may also be 
tested by rubbing a little of the dry sand in the palm of the hand; 
if the hand is nearly or quite clean after throwing the sand out, it 
is probably clean enough for mortar. The cleanness of the sand 
may be tested quantitatively by agitating a quantity of sand with 
water in a graduated glass flask; after allowing the mixture to 
settle, the amount of precipitate and of sand may be read from the 
graduation. Care should be taken that the precipitate has fully 
settled, since it will condense considerably after its upper surface is 
clearly marked. 

Sand is sometimes washed. This may be done by placing it on 
a wire screen and playing upon it with a hose; or by placing it in 
an inclined revolving screen and drenching with water. When 
only comparatively small quantities of clean sand are required, it 
can be washed by shoveling into the upper end of an inclined 
Y-shaped trough and playing upon it with a hose, the clay and 
lighter organic matter floating away and leaving the clean sand in 
the lower portion of the trough, from which it can be drawn off by 
removing for a short time plugs in the sides of the trough. Sand 
can be washed fairly clean by this method at an expense of about 
10 cents per cubic yard exclusive of the cost of the water. For a 
sketch and description of an elaborate machine for washing sand 
by paddles revolving in a box, see Engineering News , vol. xli. 
page 111 (Feb. 1G, 1899). By this method the cost of thoroughly 
washing dirty sand is about 15 cents per cubic yard. 

Although it is customary to require that only clean sand shall 
be used in making mortar, a small quantity of very finely powdered 
clay will not materially decrease the strength of the mortar. In 
some instances clay to the amount of 10 per cent, of the sand seems 
not to decrease the strength of the mortar.* Mortar containing 
considerable clay is much more dense, plastic, and water-tight; and 
is occasionally convenient for plastering surfaces and stopping leaky 
joints. Such mortar is not affected by the presence of water. 

* Report of Chief of Engineers, U. S. A., 1894, pp. 3001-10; and Trans. Amer. See, 
of C. E., vol. xiv. p. 164. 







SAND. 


[CHAP. Illtf. 


79 d 


In engineering literature but few definite specifications for the 
cleanness of sand can be found, a diligent search revealing only the 
following: For bridge work on the New York Central and Hudson 
River R. R., the specifications required that the sand shall be so 
clean as not to soil white paper when rubbed on it. For the retain¬ 
ing walls on the Chicago Sanitary Canal, the suspended matter 
when shaken with water was limited to 0.5 per cent. For the dam 
on the Monongahela River, built under the direction of the 
U. S. A. engineers, the suspended matter was limited to 1 per 
cent. For the dam at Portage, N. Y., built by the State Engineer, 
the “ aggregate of the impurities ” was limited to 5 to 8 per cent. 
The contamination permissible in any particular case depends upon 
the cleanness of the sand available and upon the difficulty of 
obtaining perfectly clean sand. Sand employed in masonry con¬ 
struction frequently contains 5, and sometimes 10, per cent, of 
suspended matter. 

114 d. Fineness. Coarse sand is preferable to fine, since (1) the 
former has less surface to be covered and hence requires less 
cement; and (2) coarse sand requires less labor to fill the interstices 
with the cement. The sand should be screened to remove the 
pebbles, the fineness of the screen depending upon the kind of work 
in which the mortar is to be used. The coarser the sand the 
better, even if it may properly be designated fine gravel, provided 
the diameter of the largest pebble is not too nearly equal to the 
thickness of the mortar joint. 

Table lOe gives the results of a series of experiments to deter¬ 
mine the effect of the size of grains of sand upon the tensile 
strength of cement mortar. The briquettes were all made at the 
same time by the same person from the same cement and sand, the 
only difference being in the fineness of the sand. The table clearly 
shows that coarse sand is better than fine. Notice that the results 
in line 4 of the table are larger than those in line 3. This is 
probably due to the fact that the sand for line 4 has a greater range 
of sizes and consequently fewer voids. If this explanation is true, 
then since the sand in each line of the lower half of the table has 
greater variety of sizes than those in the upper half, the coarse sand 
is relatively better than appears from Table lOe. 

Table 10/ shows the fineness of natural sands employed in 
actual construction; and as the sands were to all appearances of 
the same character, this table also shows at least approximately the 




ART. 1.] 


FINENESS. 


79* 


TABLE 10e. 

Effect of Fineness of Sand upon the Tensile Strength of 1 : 0 

Cement Mortar. 


Rep. 

No. 

Sand caught between 

THE TWO SIEVES STATED 
BELOW. 

Tensile Strength, in pounds per square inch, 

AFTER 

7 Days. 

1 Mo. 

3 Mos. 

6 Mos. 

12 Mos. 

1 

No. 4 and No. 

8 

243 

442 

539 

470 

665 

2 

“ 8 

it 

16 

269 

345 

473 

512 

572 

3 

“ 16 “ 

i i 

20 

186 

250 

313 

397 

396 

4 

“ 20 “ 

t i 

30 

211 

281 

322 

402 

440 

5 

o 

CO 

it 

50 

149 

205 

238 

275 

318 

6 

“ 50 “ 

it 

75 

122 

214 

260 

275 

308 

7 

“ 75 “ 

it 

100 

98 

153 

211 

208 

253 

8 

Passing No. 100 

98 

155 

161 

229 

271 


TABLE 10/. 

Tensile Strength of a 1:3 Cement Mortar with Natural Sands 

DIFFERING CHIEFLY IN FINENESS. 



Fineness. 

a 

H • 

O Z 

Z ” 

Sep. 

So. 

Per Cent., by weight, caught on Sieve No. 

Per 

Cent 

S o» 

£ CO 

m oj 


4 

8 

16 

20 

30 

50 

75 

100 

passing 

No. 

100. 

Kg 
z ® 

K J 

Eh 

1 

0 

26 

21 

16 

11 

9 

8 

7 

2 

700 

2 

0 

29 

29 

13 

10 

12 

5 

1 

1 

447 

3 

0 

22 

21 

11 

17 

20 

8 

1 

1 

370 

4 

0 

13 

15 

10 

19 

33 

6 

1 

1 

341 

5 

0 

9 

10 

6 

11 

45 

15 

2 

1 

332 

6 

0 

13 

15 

7 

8 

38 

15 

4 

1 

309 

7 

0 

0 

0 

0 

1 

6 

69 

23 

2 

246 

8 

0 

0 

0 

0 

0 

0 

0 

6 

94 

200 

9 

0 

0 

0 

2 

3 

15 

45 

30 

5 

189 




























































SAND. 


[chap, hi a. 


79/ 

effect of fineness upon tensile strength. This table agrees with 
the preceding in showing that the coarser sand makes the stronger 
mortar. This conclusion is perfectly general. 

If the voids are filled with cement, uniform coarse grains give 
greater strength than coarse and fine mixed; or, in other words, 
for rich mortar coarse grains are more important than small voids. 
But if the voids are not filled, then coarse and fine sand mixed give 
greater strength than uniform coarse grains; or, in other words, 
for lean mortar a small proportion of voids is more important than 
coarse grains.* 

As a rule, the sand ordinarily employed in making cement 
mortar is much too fine for to give maximum strength or to permit 
the use of a minimum amount of cement. For example, the sands 
in lines 13 and 14 of Table lOy (page 79 i) are much used in actual 
work, and have approximately the same degree of fineness as the 
sands in the last three lines of Table 10/, which give a much weaker 
jmortar than the preceding sands of Table 10/. 

114e. Specifications seldom contain any numerical requirement 
for the fineness of the sand. The two following are all that can 
be found. For the retaining-wall masonry on the Chicago Sanitary 
Canal the requirements were that not more than 50 per cent, shall 
pass a No. 50 sieve, and not more than 12 per cent, shall pass a 
No. 80 sieve. For the Portage Dam on the Genesee River, built 
by the New York State Engineer, the specifications were that at 
least 75 per cent, should pass a No. 20 sieve and be caught on a 
No. 40. 

The fineness of the sand employed in several noted works is as 
follows, the larger figures being the number of the sieve, and the 
smaller figures preceding the number of a sieve being the per cent, 
retained by that sieve, and the small number after the last sieve 
number being the per cent, passing that sieve: Poe Lock, 
St. Mary’s Fall Canal, 6 20 15 30 35 40 45 ; concrete for pavement 
foundations in the City of Washington, D. C., 0 3 7 6 8 8 13 10 30 20 33 
40 7 G0 3 80 1 ; Genesee (N. Y.) Storage Dam, 0 20 8 30 54 50 34 
100 4 ; Rough River (Ky.) Improvement, 11 20 14 30 53 50 22 ; St. Regis 
sand, Soulanges Canal, Canada, 12 20 26 30 51 50 11 ; Grand Coteau 


* Report of Chief of Engineers, U. S. A., 1896, p. 2862, or Jour. West. Soc. of 
Engrs., vol. ii. p. 519; and Report of Operations of the Engineering Department of 
the District of Columbia, 1896, p. 195. 







ART. 1.] 


VOIDS. 


79 g 




sand,* Soulanges Canal, Canada, 14 20 30 30 27 50 30 .. Tables 10/ and 
10<7 show the fineness of a number of natural sands employed in 
actual work. 

114/ Voids. The smaller the proportion of voids, i.e ., the 
interstices between the grains of the sand, the less the amount of 
cement required, and consequently the more economical the sand. 

The proportion of voids may be,determined by filling a vessel 
with sand and then determining the amount of water that can be 
put into the vessel with the sand. This quantity of water divided 
by the amount of water alone which the vessel will contain is the 
proportion of voids in the sand. The quantities of water as above 
may be determined by volumes or by weight. The proportion of 
voids may be determined for the sand loose or rammed, the latter 
being the more appropriate, since the mortar is either compressed 
or rammed when used. In either case it is more accurate to drop 
the sand through the water than to pour the water upon the sand, 
since with the latter method it is difficult to eliminate the air- 
bubbles,—particularly if the sand be first rammed. If the sand is 
dirty and the water is poured upon it, there is liability of the clay’s 
being washed down and puddling a stratum which will prevent the 
water penetrating to the bottom. If the bubbles are not excluded, 
or if the water does not penetrate to the bottom, the result obtained 
is less than the true proportion of voids. Again, if the sand is 
dropped through a considerable depth of water, there is liability 
that the sand may become separated into strata having a single size 
of grains in each, in which case the voids will be greater than if 
the several sizes were thoroughly mixed. 

The per cent, of voids varies with the moisture of the sand. 
A small per cent, of moisture has a surprising effect upon the 
volume and consequently upon the per cent, of voids. For 
example, fine sand containing 2 per cent, of moisture uniformly 
distributed has nearly 20 per cent, greater volume than the same 
sand when perfectly dry. This- effect of moisture increases with 
the fineness of the sand and decreases with the amount of water 
present. 

114 g. Table 10<7, page 791, shows the voids of a number of both 
artificial and natural sands. An examination of the table shows 

*A 1 to 2 mortar with this sand was only 79 per cent, as strong as the pre¬ 
ceding ; and with a 1 to 3 mortar only 71 per cent.—Trans. Can. Soc. of C. E., vol. ix, 
p. 297. 







79 h 


SAHD. 


[chap, hi a. 


that the voids of natural sand when rammed vary from 30 to 37 
per cent. Sands Nos. 10, 11, and 12 are very good; but Nos. 13 
and 14 are very poor. All five are frequently employed in actual 
work. Compare the fineness of these sands with those in Table 
10/, page 79e. 

114A. The following observations may be useful in investigating 
the relative merits of different sands: 

The proportion of voids is independent of the size of the 
•grains, but depends upon the gradation of the sizes; and varies 
with the form of the grains and the roughness of the surface. A 
mass of perfectly smooth spheres of uniform size would have the 
•same proportion of voids, whether the spheres be large or small. 
A mass of perfectly smooth spheres packed as closely as possible 
would have 26 per cent, of voids; but if the spheres are packed as 
loosely as possible the voids would be 48 per cent. A promiscuous 
mass of bird-shot has about 36 per cent, of voids. The difference 
between this and the theoretical minimum per cent., for perfectly 
smooth spheres is due to the variation in size, to roughness of the 
surface, and to not securing in all parts of the mass the arrangement 
of the shot necessary for minimum voids. German standard sand 
has grains nearly spherical and nearly uniform in size, having 
slightly rough surface, and has 41 per cent, voids loose (see line 2, 
Table 10 g). The difference in the per cent, of voids between this 
sand and a mass of spheres uniform in size and perfectly spherical 
is due to irregularities in form and to roughness of surface of the 
sand grains, and to not securing the arrangement of the grains 
necessary for minimum voids. Crushed stone retained between the 
same sieves as German standard sand has 55 per cent, of voids (see 
lines 1 to 3 of Table 10y), the excess of this over German standard 
sand being due to the rough surfaces and sharp corners preventing 
the grains from fitting closely together. 

If the mass consists of a mixture of two sizes such that the 
•smaller grains can occupy the voids between the larger, then the 
proportion of voids may be very much smaller than with a single 
•size of grains. For this reason a mixture of two grades of sand of 
widely different sizes has a smaller per cent, of voids than any one 
size alone,—compare lines 1 to 9 with the remainder of Table lOg. 

The best sand is that which has grains of several sizes such that 
the smaller grains fit into the voids of the larger, the proportion of 
any particular size being only sufficient to fill the voids between 




Fineness, Voids, and Weight of Sands for Mortar. 


ART. 1.] 


VOIDS 


79i 


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79/ 


SAND. 


[CHAP. Illrt. 


the grains of the next larger size. If the grains are spherical and 
the diameter of the smaller is about one fifth of the diameter of the 
larger, the smaller grains will just fit into the interstice between 
the larger ones. The smaller the voids the greater the economy, 
and the denser and stronger the mortar. 

The finer the sand the more nearly uniform the size of the 
grains, and consequently the less the proportion of voids. On the 
other hand, the finer the sand the less sharp it is and the greater 
the surface to be covered. Since it has been conclusively shown 
that the coarser the sand the better, the argument in favor of fine 
sand is not as potent as that against it. Farther, the advantage of 
coarse sand over fine increases as the proportion of cement 
decreases, since with the smaller proportions of cement the voids 
are not filled. 

1141. Conclusion. An examination of the preceding data shows 
that very fine sand makes a much weaker mortar than coarse sand, 
and also that natural sands vary considerably in the proportion of 
voids and consequently differ in the amount of cement required to 
produce any particular strength. Therefore before adopting a sand 
for a work of any considerable magnitude, all available sands should 
be carefully examined with reference to (1) their effects upon the 
strength of the mortar, (2) their per cent, of voids or the amount 
of cement required with each, and (3) their cost. If mortar of any 
particular strength is desired, the proportion of cement should be 
adjusted according to the fineness and voids of the best available 
sand. 

114/. Stone Screenings. The finer particles screened out of 
crushed stone are sometimes used instead of sand. For the physical 
characteristics of stone screenings see Nos. 1G and 17, page 79t. • 

Experiments show that sandstone screenings give a slightly 
stronger mortar than natural sand, probably because of the greater 
sharpness of the grains. Crushed limestone usually makes a con¬ 
siderably stronger mortar, in both tension and compression, than 
natural sand, and this difference seems to increase with the age of 
the mortar.* Part of the greater strength is unquestionably due 
to the greater sharpness of the limestone screenings, and the part 


* Annual Report of Chief of Engineers, U. S. A., 1893, Part 3, p. 3015 ; do. 1894, 
Part 4, p. 2321; do. 1895, Part 4, p. 2953; Jour. West. Soc. of Engrs., vol.' ii, pp. 394 
and 400. 






ART. 2.] 


GRAVEL. 


79 h 


that increases with the age of the mortar seems to be due to some 
chemical action between the limestone and the cement. 

114&. Cost and Weight of Sand. The price of reasonably good 
sand varies from 40 cents to $1.60 per yard, according to locality. 

Sand is sometimes sold by the ton. It weighs, when dry, from 
80 to 115 pounds per cubic foot (see Table 10#, page 79f), or about 
1 to 1^ tons per cubic yard. 

Art. 2. Gravel and Broken Stone. 

115. The term gravel is sometimes used as meaning a mixture 
of coarse pebbles and sand, and sometimes as meaning pebbles with¬ 
out sand. In this volume, gravel will be understood as a mixture 
of coarse pebbles and sand. 

115^. Gravel and broken stone are mixed with cement mortar 
to make an artificial stone called concrete (Art. 2, Chap. IV). The 
quality of the concrete varies greatly with the condition of the 
gravel or broken stone, but unfortunately too little attention is 
given to the character of this component. 

1156. Gravel. To be suitable for use in making concrete, 
gravel should be clean, and it should be composed of durable 
minerals, and the size of the pebbles and grains should be such as 
to give minimum voids. 

The investigation of the suitability of gravel for use in concrete 
is essentially the same as that of sand, which has been fully con¬ 
sidered in the preceding article. 

The physical characteristics of pebbles and gravel are given near 
the foot of Table 10/*, page 80, Judging from the little data that 
can be found in engineering literature and from all the information 
gathered by an extensive correspondence, gravels No. 16 and No. 
17 of the table are representative of the gravels employed in actual 
work. 

Concerning No. 18 notice that 65 per cent, passed a No. 5 
screen; and therefore this mixture could more properly be called 
gravelly sand. If one fifth of the material passing the No. 5 sieve 
be omitted, the voids of the remainder will be only 15 per cent, 
when rammed ; in other words, if one-tenth of this gravel were 
sifted on a No. 5 sieve and that portion retained on the sieve were 
mixed with the remainder of the original, the voids would be 
reduced to 15 per cent., which would improve the quality of the 



BROKEN STONE. 


[chap. Ill a. 


79 1 


gravel for making concrete. This is a valuable hint as to the pos¬ 
sible advantage of sifting even a portion of the gravel. 

115 c . Broken Stone. Any hard and durable stone is suitable 
for use in making concrete. It is usual to specify that the stone 
for concrete shall be broken to pass, every way, through a 2-inch 
ring, although it is sometimes broken to pass a 1-inch ring. The 
stone should be broken small enough to be conveniently handled 
and easily incorporated with the mortar. The finer the stone is 
broken the greater its cost, and the greater the surface to be coated; 
and consequently the greater the amount of cement required. 
Approximately cubical pieces are preferable to long, thin, splintery 
fragments, since the latter are liable to break under pressure or 
while being rammed into place, and thus leave two uncemented 
surfaces. 

115 d. Voids. The jiroportion of voids, i.e., interstices between 
the fragments, may be determined in either of two ways as follows: 

1. The voids may be found by filling a vessel with the aggregate, 
and then pouring in water until the vessel is full. The amount of 
w r ater required to fill the voids divided by the amount of water 
alone the vessel will contain is the proportion of voids in the 
aggregate. The amount of water in each case may be determined 
by weight or by volume. 

For some precautions applicable in this case, particularly in 
determining the voids of broken stone containing considerable fine 
material, see § 114/. If the material is porous, it is best to wet it, 
so as to determine the voids exterior to the fragments. The water 
absorbed by the material should not be included in the voids, since 
wdien the concrete is mixed the aggregate is usually dampened, 
particularly if it is porous; Of course in wetting the aggregate 
before determining the voids no loose water should remain in the 
pile. The voids may be determined for the material either loose 
or compacted. The proportion of the voids is found to determine 
the amount of mortar required to fill the voids of the concrete in 
place; and therefore it is better to determine the voids in the com¬ 
pacted mass, since the concrete is usually rammed when laid. The 
compacting may be done by shaking or by ramming, the latter 
being the better since it 'more nearly agrees with the conditions 
under which the concrete is used, and further since in compacting 
by shaking the smaller pieces work to the bottom and the larger to 
the top, which separation increases the voids. 




ART. 2.] 


VOIDS. 


79m 


This method usually gives results slightly too small, owing to 
the difficulty of excluding all the air-bubbles. However, a high 
degree of accuracy can not be expected, since the material is neither 
’ uniform in composition nor uniformly mixed. 

2. To find the voids determine the specific gravity of a frag¬ 
ment of the material (§ 7), and from that the weight of a unit of 
volume of the solid; and also weigh a unit of volume of the aggre¬ 
gate. The difference between these weights divided by the first 
gives the proportion of voids. 

115?. Table 107*, page 80, shows the per cent, of voids in 
various grades of broken stones used in making concrete. 

The per cent, of voids in broken stone varies with the hardness 
of the stone, the form of the fragments, and the relative propor¬ 
tions of the several sizes present. The last is the most important. 
If broken stone passing a 3J-inch ring and not a J-inch screen 
be separated into three sizes, any one size will give from 52 to 54 
per cent, of voids loose, while equal parts of any two of the three 
sizes will give 48 to 50 per cent., and a mixture in which the 
volume of the smallest size is equal to the sum of the other two 
gives a trifle less than 48 per cent. Notice, however, that un¬ 
screened crushed stone has only 32 to 35 per cent, voids—see lines 
7 and 11 of Table 107*. This is a very excellent reason for not 
screening the broken stone to be used in making concrete. 

A mass of pebbles has only about three fourths as many voids 
as a mass of broken «stone having pieces retained between the same 
screens. Notice, however, that gravel, i.e. pebbles and sand, has a 
less proportion of voids than pebbles alone. 

115/. Cost and Weight. The cost of breaking stone for con¬ 
crete varies from 50 to 75 cents per cubic yard according to kind 
of stone and size of plant.* The original cost of the stone and 
transportation expenses are too variable to attempt to generalize. 
Ordinarily the cost of broken stone is not more than $1.50 to $2.00 
per cubic yard f. o. b. cars at destination. 

The weight of broken stone varies from 85 to 120 lbs. per cubic 
foot (see Table 107*, page 80); or about 2200 to 3200 pounds per 
cubic yard. 


* For additional data, see Supplemental Notes, No. 5, p. 546. 






TABLE m 

Voids and Weight of Gravel and Broken Stone for Concrete. 

Arranged in the order of the voids. 


80 


BROKEN" STONE. 


[CHAP. Ill a. 


Weights, Lbs. 

PER CU. FT. 

Rammed. 

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PART II. 


METHODS OF PREPARING AND USING THE 

MATERIALS. 


CHAPTER IV. 

MORTAR, CONCRETE, AND ARTIFICIAL STONE. 

Art. 1. Mortar. 

116. Mortar is a mixture of the paste of cement or lime with 
sand. In common mortar, the cementing substance is ordinary 
lime; in hydraulic mortar, it is hydraulic cement. 

117. Common Lime Mortar. Mortar made of the paste of 
common or fat lime is extensively used on account of (1) its intrin¬ 
sic cheapness, (2) its great economic advantage owing to its great 
increase of volume in slaking, and (3) the simplicity attending the 
mixing of the mortar. On account of the augmentation of volume, 
the paste of fat lime shrinks in hardening, to such an extent that 
it can not be employed as mortar without a large dose of sand. 

As a paste of common lime sets or hardens very slowly, even in 
the open air, unless it be subdivided into small particles or thin 
films, it is important that the volume of lime paste in common 
mortar should be but slightly in excess of what is sufficient to coat 
all the grains of sand and to fill the voids between them. If this 
limit be exceeded, the strength of the mortar will be impaired. 
With most sands the proper proportions will be from 2.5 to 3 
volumes of sand to 1 volume of lime paste. Generally* if either 
less or more sand than this be used, the mortar will be injured,— 
in the former case from excess of lime paste, and in the latter from 

81 



MORTAR. 


[CHAP. IV*. 


J32 

porosity. Notice that the volume of the resulting mortar is about 
equal to the volume of the sand alone. 

118. The ordinary method of slaking lime consists in placing 
the lumps in a layer G or 8 inches deep in either a water-tight box, 
or a basin formed in the sand to be used in mixing the mortar, and 
pouring upon the lumps a quantity of water 2^ to 3 times the 
volume of the lime. 

This process is liable to great abuse at the hands of the work¬ 
men. They are apt either to use too much water, which reduces 
the slaked lime to a semi-fluid condition and thereby injures its 
binding qualities; or, not having used enough water in the first 
place, to seek to remedy the error by adding more after the slaking 
has well progressed and a portion of the lime is already reduced to 
powder, thus suddenly depressing the temperature and chilling the 
lime, which renders it granular and lumpy. It is also very im¬ 
portant that the lime should not be stirred while slaking. The 
essential point is to secure the reduction of all the lumps. Cover¬ 
ing the bed of lime with a tarpaulin or with a layer of sand retains 
the heat and accelerates the slaking. All the lime necessary for 
any required quantity of mortar should be slaked at least one day 
before it is incorporated with the sand. 

After the lime is slaked the sand is spread evenly over the paste, 
and the ingredients are thoroughly mixed with a shovel or hoe, a 
little water being added occasionally if the mortar is too stiff. 

119. Mortar composed of common lime and sand is not fit for 
thick walls, because it depends upon the slow action of the atmos¬ 
phere for hardening it; and, being excluded from the air by the 
surrounding masonry, the mortar in the interior of the mass 
hardens only after the lapse of years, or perhaps never.* The 
mortar of cement, if of good quality, sets immediately; and, as far 
as is known, continues forever to harden without contact with the 
air. Cement mortar is the only material whose strength increases 
with age. Owing to its not setting when excluded from the air, 
common lime mortar should never be used for masonry construction 
under water, or in soil that is constantly wet; and, owing to its 
weakness, it is unsuitable for structures requiring great strength, or 

*Lime mortar taken from the walls of ancient buildings has been found to bo 
only 50 to 80 per cent, saturated with carbonic acid after nearly 2,000 years of ex¬ 
posure. Lime mortar 2,000 years old has been found in subterranean vaults, in 
exactly the condition, except for a thin crust on top, of freshly mixed mortar. 






ART. 1.] 


METHODS OF PROPORTIONING. 


83 


subject to shock. Its use in engineering masonry has been aban¬ 
doned on all first-class railroads. Cement is so cheap that it could 
profitably be substituted for lime in the mortar for ordinary 
masonry. 

120. Hydraulic Lime Mortar. With mortars of hydraulic 
lime the volume of sand should not be less than 1.8 times that of 
the lime paste, in order to secure the best results regardless of cost.. 
The usual proportions are, however, for ordinary work, the same 
as in common mortars, care being taken to incorporate sufficient 
paste to coat all the grains of sand and to fill up the voids between 
them. 

121. Hydraulic Cement Mortar. Hydraulic cement mortar 
hardens simultaneously and uniformly throughout the mass, and if 
the cement is good continues to gain in hardness with age,—the 
slow-setting cements for a longer time than the quick-setting. For 
the best results the cement paste should be just sufficient to coat 
the grains and fill the voids of the sand. More cement than this 
adds to the cost and weakens the mortar (see § 100). If the amount 
of cement is not sufficient to coat all the grains and fill the voids, 
the mortar will be weak and porous, and hence will not be durable. 
A dense, impervious mortar is particularly desirable for masonry 
exposed to sea-water, to exclude the water from the interior of the 
mass and prevent its chemical as well as physical action upon the 
cement. 

122. Methods of Proportioning. In laboratory work the propor¬ 
tions of the cement and sand are uniformly determined by weigh¬ 
ing; but there is no uniform practice of measuring the proportions 
on the work. One of the three following methods is generally 
employed. 

1. By Weight. The most accurate but least common method 
is to weigh the ingredients for each batch. This method is incon¬ 
venient in practice, and adds somewhat to the cost of the work; 
and therefore occasionally the weight of a unit of volume of the 
sand and of the cement is determined, and the relative volumes of 
the ingredients are fixed accordingly, the actual proportioning being 
done by volumes, Cement is bought and sold by weight, and 
hence it is very appropriate to proportion the mortar by weight. 

2. Packed Cement and Loose Band. A commercial barrel of 
cement is mixed with one or more barrels of loose sand, i.e., the 
proportioning is done by mixing one volume of packed cement with 



84 


MORTAR. 


[CHAP. IT. 


one or more volumes of loose sand. This method is frequently 
used. As far as the cement is concerned, it is as accurate as the 
first, since the weight and volume of a barrel of cement may readily 
be known when only whole barrels are used,—as is usually the case. 
Even though the cement is received in bags, the barrel of packed 
cement is still a convenient unit, for an integral number of bags, 
usually three or four, are equal in weight to a barrel. As far as 
the sand is concerned this method is not as accurate as the first. 
The weight of the sand is affected by the amount of moisture 
present; but a small amount of moisture affects the volume in a 
greater proportion than the weight. For example, the addition of 
2 per cent, of water (by weight) thoroughly mixed with dry sand 
increases the volume of the sand nearly 20 per cent.* Therefore if 
the mortar is proportioned by volumes, damp sand will give a richer 
mortar than dry sand. The effect of moisture on the volume is 
greater the finer the sand, and decreases as the amount of moisture 
increases. Measuring the sand by volumes is inaccurate also owing 
to the packing of the sand. 

Except for the inaccuracies in measuring the sand, this method 
gives practically the same results for Portland as the first method, 
since ordinarily a unit of volume of packed cement and of sand 
weighs substantially the same; viz., 100 pounds per cubic foot. 
Since natural cement when packed in barrels usually weighs about 
75 pounds per cubic foot, a mortar of 1 part natural cement to 
1 part sand by weight is equivalent to 1-^ parts cement to 1 part 
sand by volumes of packed cement and loose sand. 

3. Loose Cement and Loose Sand. A volume of loose cement is 
mixed with one or more volumes of loose sand. The actual propor¬ 
tioning is usually done by emptying a bag or fractional part of a 
barrel of cement into a wheelbarrow, and filling one or more wheel¬ 
barrows equally full of sand. As far as the sand is concerned, this 
method is as inaccurate as the second; and it is also subject to great 
variations owing to differences in specific gravity, fineness and 
packing of the cement. Even though inaccurate, it is very fre¬ 
quently employed. It is the most convenient method when the 
cement is shipped in bulk,—which is only rarely. 

Occasionally the actual proportioning is done by throwing into 

* Feret, Chief of Laboratory Ponts et Chaussees, in Engineering News, vol. 
-xxYii. p. 310. For similar data see Report of Chief of Engineers, U. S. A., 1895 
p. 2935. 






ART. 1.] 


MIXING THE MORTAR. 


85 


the mortar-box one shovelful of cement to one or more shovelfuls 
of sand. This is very crude, and should never be permitted. 

Since a commercial barrel of Portland will make 1.1 to 1.4 
barrels if measured loose, a mortar composed of 1 part Portland 
cement to 1 part sand, by weight, is equivalent to 0.7 to 0.8 parts 
cement to 1 part sand by volumes of loose cement and loose sand; 
and a mortar composed of 1 part natural cement to 1 part sand, 
by weight, is equivalent to 0.50 to 0.75 parts cement to 1 part of 
sand by volumes of loose cement and loose sand. 

122 a. For a tabular statement incidentally showing the relative 
amounts of cement required by the three methods of proportioning, 
see Table 11, page 88. 

123 . Proportions in Practice. The proportions commonly used 
in practice are: for Portland cement, 1 volume of cement to 2 or 3 
volumes of sand; and for natural cement, 1 volume of cement to 1 
or 2 volumes of sand. The specifications are usually defective in 
not defining which method is to be employed in proportioning. 
This is a matter of great importance. Compared with the second 
method of proportioning in § 129, the third requires for Portland 
only 0.7 to 0.8 as much cement, and for natural cement only 0.4 
to 0.5 as much. 

124 . Mixing the Mortar. When the mortar is required in small 
quantities, as for use in ordinary masonry, it is mixed as follows: . 
About half the sand to be used in a batch of mortar is spread evenly 
over the bed of the mortar-box, then the dry cement is spread 
evenly over the sand, and finally the remainder of the sand is 
spread on top. The sand and cement are then mixed with a hoe 
or by turning and re-turning with a shovel. The mixing can be 
done more economically with a shovel than with a hoe; but the 
effectiveness of the shovel varies greatly with the manner of using 
it. It is not sufficient to simjfiy turn the mass; but the sand and 
cement should be allowed to run off from the shovel in such a 
manner as to thoroughly mix them. Owing to the difficulty of 
getting laborers to do this, the hoe is sometimes prescribed. If 
skillfully done, twice turning with a shovel will thoroughly mix 
the dry ingredients; although four turnings are sometimes specified, 
and occasionally as high as six (see § 260). It is very important 
that the sand and cement be thoroughly mixed. When thoroughly 
mixed it will have a uniform color. 

The dampness of the sand is a matter of some importance. If 



86 


MORTAR, 


[CHAP. IV, 


the sand is very damp when it is mixed with the cement, sufficient 
moisture may be given oft to cause the cement to set partially, 
which may materially decrease its strength. This is particularly 
noticeable with quick-setting cements. 

The dry mixture is then shoveled to one end of the box, and 
water is poured into the other. The sand and cement are then 
drawn down with a hoe, small quantities at a time, and mixed with 
water until enough has been added to make a stiff paste. The 
mortar should be vigorously worked to insure a uniform product. 
When the mortar is of the proper plasticity the hoe should be clean 
when drawn out of it, or at most but very little mortar should stick 
to the hoe. 

Cements vary greatly in their capacity for water (see § 104), the 
naturals requiring more than the Portlands, and the fresh-ground 
more than the stale. An excess of water is better than a deficiency, 
particularly with a quick-setting cement, as its capacity for com¬ 
bining with water is very great; and farther an excess is better than 
a deficiency, owing to the possibility of the water evaporating 
before it has combined with the cement. On the other hand, an 
excess of water makes a porous and weak mortar. If the mortar is 
stiff, the brick or stone should be dampened before laying; else the 
brick will absorb the water from the mortar before it can set, and 
. thus destroy the adherence of the mortar. In hot dry weather, the 
mortar in the box and also in the wall should be shielded from the 
direct rays of the sun. 

When mortar is required in considerable quantities, as in making 
concrete, it is usually mixed by machinery (see § 156?a). 

125. Grout. This is merely a thin or liquid mortar of lime or 
cement. The interior of a wall is sometimes laid up dry, and the 
grout, which is poured on top of the wall, is expected to find its 
way downwards and fill all voids, thus making a solid mass of the 
wall. Grout should never be used when it can be avoided. If 
made thin, it is porous and weak; and if made thick, it fills only 
the upper portions of the wall. To get the greatest strength, the 
mortar should have only enough water to make a stiff paste—the 
less water the better. 

126. Bata for Estimates. The following will be found use¬ 
ful in estimating the amounts of the different ingredients necessary 
to produce any required quantity of mortar: 

Lime weighs about 230 pounds per barrel. One barrel of lime 






ART. 1.] 


DATA FOR ESTIMATES. 


87 


will make about barrels (0.3 cu. yd.) of stiff lime paste. One 
barrel of lime paste and three barrels of sand will make about 
three barrels (0.4 cu. yd.) of good lime mortar. One barrel of 
unslaked lime will make, about 6.75 barrels (0.95 cu. yd.) of 1 
to 3 mortar. 

Portland cement weighs 370 to 380 pounds per barrel net (see 
§ 77, page 54). The capacity of a Portland cement barrel vaiies 
from 3.20 to 3.75 cu. ft., the average being 3.49* or practically 

3.50 cu. ft. A barrel of Portland willmake from 1.1 to 1.4 bar¬ 
rels if measured loose. A cubic foot of packed Portland cement 
(105 pounds) and about 0.33 cu. ft. of water will make 1 cu. ft. of 
stiff paste; and a cubic foot of loose cement (gently shaken down 
but not compressed) will make about 0.8 cu. ft. of stiff paste. 

Natural cement weighs from 265 to 300 pounds per barrel net 
(see § 77, page 54). The capacity of a natural cement barrel varies 
from 3.37 to 3.80 cu. ft., the average being 3.52,* or practically 

3.50 cu. ft. A barrel of natural cement will make from 1.33 to 

1.50 barrels if measured loose. Volume for volume, natural 
cement will make about the same amount of paste as Portland; or 
a cubic foot of packed natural cement (75 pounds) and about 0.45 
cu. ft. of water will make 1 cu. ft. of stiff paste, and a cubic foot 
of loose cement (gently shaken down, but not compressed) will 
make about 0.8 cu. ft. of stiff paste. 

128. Quantities for a Yard of Mortar. Table 11, page 88, 
sIioavs the approximate quantities of cement and sand required for 
a cubic yard of mortar by the three methods of proportioning 
described in § 122. The table is based upon actual tests made by 
mixing 3J cubic feet of the several mortars; f but at best such data 
can be only approximate, since so much depends upon the specific 
gravity, fineness, compactness, etc., of the cement; upon the fine¬ 
ness, humidity, sharpness, compactness, etc., of the sand; and 
upon the amount of water used in mixing. The sand employed in 
deducing Table 11 contained 37 per cent, of voids when measured 
loose; and the plasticity of the mortar was such that moisture 
flushed to the surface when the mortar was struck with the back 
of the shovel used in mixing. 

The volume of the resulting mortar is always less than the sum 

* The Technograph, University of Illinois, No. 11, p. 104. 
f By L. C. Sabin, Assistant U. S. Engineer—see Report of Chief of Engineers, 
U. S. A., 1894, p. 2326. 






Cement and Sand required for 1 Cubic Yard of Mortar. 


88 


MORTAR 


[CHAP. IV, 




































































AKT. 1.] 


DATA FOR ESTIMATES. 


89 


TABLE 12. 

Amount of Mortar required for a Cubic Yard of Masonry. 


1 

Ref. 

No. 

Description of Masonry. 

Mortar, 
cu. yd. 


Min. 

Max. 

1 

Ashlar,—18" courses and 1" joints. 

0.03 

0.04 

2 

12" “ “ “ “ . 

0.06 

0.08 

3 

Brickwork,—standard size (§ 256) and 4" joints .... 

0.10 

0.15 

4 

“ “ “ “ |" top' “ .... 

0.25 

0.35 

5 

“ “ “ “ |" to “ _ 

0.35 

0.40 

6 

7 

Concrete—see Tables 13d and 13e, pages 112^, 112/i. 

Bubble —small, rouerh stones. 

0.33 

0.40 

8 

large stones, rough hammer-dressed. 

0.20 

0.30 

9 

Squared-stone masonry,—18" courses and £" joints_ 

0.12 

0.15 

10 

12" “ “ “ “ 

0.20 

0.25 


of the volumes of the cement and sand, or of the paste and sand, 
because part of the paste enters the voids of the sand; but the 
volume of the mortar is always greater than the sum of the volumes 
of the paste and the solids in the sand, because of imperfect mixing 
and also because the paste coats the grains of sand and thereby 
increases their size and consequently the volume of the interstices 
between them. This increase in volume varies with the dampness 
and compactness of the mortar. For example, the volume of a 
rather dry mortar with cement paste equal to the voids, when 
compacted enough to exclude great voids, was 126 per cent, of the 
sum of the volumes of the paste and solids of the sand; and the 
same mortar when rammed had a volume of 102 to 104 per cent. 
If the paste is more than equal to the voids, the per cent, of in¬ 
crease is less; and if the paste is not equal to the voids, the per cent, 
of increase is more. The excess of the volume of the mortar over 
that of the sand increases with the fineness of the sand and with 
the amount of mortar used in mixing. 

129. Mortar for a Yard of Masonry. Table 12, page 89, gives 

















$0 


MORTAR. 


[CHAP. IY. 


data concerning the amount of mortar required per cubic yard for 
the different classes of masonry, extracted from succeeding pages 
of this volume; and are collected here for greater convenience in 
making estimates. 

130. Strength of Mortar. The strength of mortar is 
dependent upon the strength of the cementing material, upon the 
strength of the sand, and upon the adhesion of the former to the 
latter. The kind and amount of strength required of mortar 
depends upon the kind and purpose of the masonry. If the blocks 
are large and well dressed, and if the masonry is subject to com¬ 
pression only, the mortar needs only hardness or the property of 
resisting compression; hard sharp grains of sand with comparatively 
little cementing material would satisfy this requirement fairly well. 
If the blocks are small and irregular, the mortar should have the 
capacity of adhering to the surfaces of the stones or bricks, so as to 
prevent their displacement; in this case a mortar rich in a good 
cementing material should be used. If the masonry is liable to be 
subject to lateral or oblique forces, the mortar should possess both 
adhesion and cohesion. 

131. Tensile Strength. Fig. 5 shows the effect of time upon 
the strength of various mortars. The diagram represents the 
average results of a great number of experiments made in connec¬ 
tion with actual practice. Results which were uniformly extremely 
high or low as compared with other experiments were excluded on 
the assumption that the difference was due to the method of mould¬ 
ing and testing. Since the individual values plotted were them¬ 
selves means, there were no very erratic results, and consequently 
the lines are quite reliable. There were fewer experiments for the 
larger proportions of sand to cement, and hence the curves are less 
accurate the larger the proportion of sand. 

The line for the strength of lime mortar probably represents the 
maximum value that can be obtained by exposing the mortar freely 
to the air in small briquettes. This line is not well determined. 

Unusually hard-burned Portland cements when tested neat 
will show a greater strength than that given in the diagrams. 
Very fine cement when mixed with sand will show greater strength 
than that given by Fig. 5. Again, the diagram shows neat cement, 
both Portland and natural, stronger than any proportion of sand, 
while frequently neat cement mortar is not as strong as a mortar 
composed of one part sand and one part cement—particularly at 




ART. 1.] 


TENSILE STRENGTH. 


91 


the greater ages. However, notwithstanding these exceptions, it 
is believed that the results represent fair average practice. The 
proportions of sand to cement were determined by weight. 

132. The results in Fig. 5 are tabulated in another form in 
Fig. 6, to show the effect of varying the proportions of the sand 



and cement, and also to show the relative strength of natural and 
Portland cement mortars at different ages. The curves of Fig. 6 
are especially useful in discussing the question of the relative 
economy of Portland and natural cement (§ 13G). For example, 
assume that we desire to know the strength of a 1 to 2 natural 
cement mortar a year old, and also the proportions of a Portland 
cement mortar of equal strength. At the bottom of the lower 


























92 


MORTAR. 


[chap. IV. 

right-hand diagram of Fig. G find the proportion of sand in the 
mortar, which in this case is 2; follow the corresponding line up 
until it intersects the “ natural ” line. The elevation of this in¬ 
tersection above the base, as read from the figure at the side of 
the diagram, is the strength of the specified mixture, which in this 



Fig. 6.—Diagram showing Relative Strength of Cement Mortars. 

/ 


case is about 250 pounds per square inch. The second part of the 
problem then is to determine the proportions of a Portland cement 
mortar which will have a strength of 250 pounds per square inch. 
Find the 250 point on the scale at the side of the diagram, and 
imagine a horizontal line passing through this point and intersect- 
























































































































ART. 1.] 


COMPRESSIVE STRENGTH. 


93 


ing the “ Portland ” line; from this point of intersection draw a 
vertical line to the base of the diagram, and this point of intersec¬ 
tion gives tlie required number of volumes of sand to one volume of 
cement, which in this case is 5.5. Therefore a 1 to 2 natural 
mortar a year old has a strength of 250 pounds per square inch, and 
is then equivalent to a 1 to 5.5 Portland mortar. 

133. Compressive Strength. But few experiments have been 
made upon the compressive strength of mortar. An examination 
of the results of about sixty experiments made with the Watertown 
testing-machine seems to show that the compressive strength of 
mortar, as determined by testing cubes, is from 8 to 10 times the 
tensile strength of the same mortar at the same age. This ratio 
increases with the age of the mortar and with the proportion of 
sand. The standard German specifications require that the com¬ 
pressive strength of cement mortar shall be at least 10 times the 
tensile strength. 

Data determined by submitting cu^»es of mortar to a compressive 
stress are of little or no value as showing the strength of mortar 
when employed in thin layers, as in the joints of masonry. The 
strength per unit of bed area increases rapidly as the thickness of 
the test specimen decreases, but no experiments have ever been 
made to determine the law of this increase for mortar. 

134. Adhesive Strength. Unfortunately very few experiments 
have been made on the adhesive strength of mortars, i. e ., the 
power with which mortars stick to brick, stone, etc. It is com¬ 
monly assumed that, after the lapse of a moderate time, the 
adhesive and cohesive strengths of cement mortars are about equal, 
and that in old work the former exceeds the latter. Modern 
experiments, however, fail to establish the truth of this assumption, 
and indicate rather that the adhesion of mortar to brick or stone is 
much less, during the first few months, than its tensile strength; 
and also that the relation between the adhesive strength and 
cohesive strength (the resistance of the mortar to pulling asunder); 
is very obscure. The adhesion of mortars to brick or stone varies 
greatly with the different varieties of these materials, and particu¬ 
larly with their porosity. The adhesion also varies with the quality 
of the cement, the character, grain, and quantity of the sand, the 
amount of- water used in tempering, the amount of moisture in the 
stone or brick, and the age of the mortar. Some cements which 
exhibit high tensile strength give low values for adhesion; and con- 





94 


MORTAR 


[CHAP. IY, 


TABLE 13. —Adhesive Strength of Mortars. 


Reference No. 

Age, in days,when 
tested. 

Kind of Cement used. 

Materials 
Cemented to¬ 
gether. 

Average adhesive strength in 
pounds per square inch. 

Authority 


Neat Cem¬ 

ent. 

Cement, 1; 

sand, 1. 

Cement, 1; 

sand, 2. 

Cement, 1; 

sand, 3. 

Cement, 1; 

sand. 4. 

1 


Quick-setting cement 

Hard brick. 



*23 



Robertson^. 

.1858 

2 

tf 

Slow-setting” cement. 

Hard brick. 



*15 



ft 

ii 

3 

f f 

Portland.. .” . 

Sawed limest’ne 

57 





T. J. Mann. . 

.1883 

4 

It 

ft 

Cut granite..-_ 

41 





ti if 

»i 

■5 

(1 

ft 

Polished marble 

38 





if (< 

f f 

6 

«( 

ft 

Bridgewater 











brick. 

19 





ft tf 

ff 

7 

If 

Hydraulic lime. 

+Brick. 

24.1 

21.0 

18.7 

15.3 

13.2 

Dr Rohme.. 

ff 

8 

<1 

Portland. 

X “ . 

168 

102 

38 

20 

9 

Prof. Warren 

..’87 

9 

ii 

ft 

| “ . 

117 

53 

26 

16 

ft ft 

f i 

10 

16 

Quicklime. 

Limestone. 



9-15 



Boistard. 


11 

f i 

Lime and cement. 

tf 



5 



11 


12 

28 

Hydraulic lime. 

+Brick. 

35.1 

30.4 

25.5 

20.9 

17.5 

Dr. Rhhme. . 

.1883 

13 

(i 

Portland. 

% “ . 

213 

105 

45 

24 

14 

Prof. Warren 

..’87 

14 

(1 

ft 

§ “ . 


146 

73 

48 

45 

ii ti 

if 

15 

30 

Quick-setting cement 

Hard brick. 



*59 



Robertson.... 

.1858 

16 

tf 

Slow-setting cement. 

Hard brick. 



*30 



ti 

f i 

1? 

it 

Rosendale.T. 

Croton brick_ 

30.8 

15.7 

12.3 

6.8 

5.2 

Gen. Gillmore.’63 

18 

ii 

ii 

Fine-cut granite 

27.5 

20.8 

12.0 

9.2 

7.9 

if it 

ft 

19 

( l 

Portland. 

Sawed limest’ne 

78 





I. ,T. Mann.... 

188? 

20 

(1 

ft 

Cut granite. 

1197 





ii ti 

tf 

21 

it 

ft 

Polished marble 

1171 





ft ft 

if 

22 

t< 

ti 

Bridgewater 










brick. 

||66 





if ti 

tf 

23 

ft 

ft 

Sandstone. 

49 





tf f f 

ft 

24 

tt 

Blue lias lime. 

Staffordshire 











brick. 



*40 



Ruildina News'8 0 

25 

it 

ft f< ft 

Gray stock brick 



*36 



if ti 

'it 

26 

it 

ft ft ii 

Common soft “ 



*18 



ft if 

ff 

27 

t< 

Lime and pozzuolaua 

Hard brick. 



*5 



J. White. 

.1832 

28 

42 

Portland .".. 

TTBrick. 

68.8 


46.9 



Ransehinger. 

1873 

29 

48 

it 

1 “ . 



24.2 


f f 

f f 

30 

56 

tf 

7 “ . 


54.0 

56.9 



ti 

ff 

31 

90 

Hydraulic lime. 

+ “ . 

39.3 

41.9 

38.9 

28.1 

22.6 

Dr Bohme... 

18S3 

32 

95 

Portland . 

1 “ . 



14.2 


Ransehinger. 

1873 

33 

110 

Hydraulic lime. 

IT “ . 




12.8 


ii w 

f f 

34 

180 

Quicklime. 

Brick. 



*83 



Rondelet. 

1831 

35 

ii 

ft 

Limestone. 



*15 



ii 

f f 

36 

it 

ft 

Hard brick. 



*40 



Robertson.. 

1858 

37 

it 

ft 

Soft brick. 



*18 



if 

if 

38 

ii 

Portland. 

Sawed slate. 

1162 





T. .T. Ma nn . . 

1883 

it 

39 

ft 

ii 

Portland stone.. 

|55 





f f it 

40 

it 

if 

Polished marble 

Sts 





<f ft 

ff 

41 

270 

Lime and pozzuolana 

Hard brick. 



*8 



.T White 

18.82 

42 

320 

Rosendale. 

Croton brick.... 

68 

40 

24 




43 

1 yr 

if 

Quicklime. 

Not stated. 


*21 


Vi oat. 

1818 

44 

Good quicklime. 

ii ft 




*51 


tt 

f f 

45 

if 

Ordinary hydraulic 











lime. 

ti ft 



*85 



ct 

ff 

46 

if 

Good hydraulic lime 

if if 



*140 



tt 

ff 

47 

ii 

if ti ii 

Materials in air. 


70 




Mallet. 

1829 

48 

if 

it If ft 

in water 


99 




f i 

tt 

49 

ti 

Portland. 

Gault-clay brick 











pressed. 

45 

44 




J. Grant... 

1871 

50 

ft 

ti 

Stock brick in 










air. 

78 

63 




ft 

(1 

51 

if 

ti 

Stock brick in 











water. 

96 

70 




«f 

if 

52 

ft 

II 

Staf. blue brick 











in air. 

48 

47 




ff 

ff 

53 

ft 

it 

Staf. blue brick 











in water. 

40 

29 




ff 

tt 

54 

f f 

it 

Fareham red 











brick in air.... 

126 

83 




if 

f( 

55 


ff 

Fareham red 











brick in water. 

123 

62 




ft 

ff 


* Proportions of sand not given, but presumably about those indicated in headings of table. 
+ Standard sand used in mixture. * Clean river-sand used in mixture. 

5 Crushed sandstone used in mixture. 

| Coarse particles iu cement sifted out before testing. T Fine river-sand used in mixture. 
















































































































































































































ART. 1.] 


COST OF MORTAR. 


95 


Tersely, cements which are apparently poor when tested for cohesion, 
show excellent adhesive qualities. 

The table * on the preceding page gives all the reliable data 
known. A comparison of the table with the diagram on page 92 
shows that the adhesion of a mortar is far less than its tensile 
strength at the same age, but fails to show any definite relation 
between the two. In the experiments by Dr. Bohme at the Boyal 
Testing Laboratory at Berlin the mortar was made with standard 
quartz sand, and the tensile strength of the mortar and its adhesion 
to common brick were determined separately. By comparing the 
tensile and adhesive strengths at the same ages, it was found that 
the former was always about ten times greater than the latter when 
the mortar consisted of one part of cement to three or four parts 
of sand, and from six to eight times greater when the cement was 
used neat or with one or two parts of sand. In the experiments 
made by Prof. Warren, of Sydney University, New South Wales, 
the tensile strength of neat Portland cement mortar was three and 
a half times its adhesion to brick. The result of twelve thousand 
' special tests by Mr. Mann was that pure Portland cement of 425 
pounds tensile and 5,640 pounds compressive strength per square 
inch has but 60 to 80 pounds adhesion to limestone, and that the 
ratio of tensile to adhesive strength varies from 5 to 1 to 9 to 1. 

135. Cost of Mortar. Knowing the price of the materials it 
is very easy, by the use of Table 11, page 88, to compute the cost 
of the ingredients required for a cubic yard of mortar. The 
expense for labor is quite variable, depending upon the distance the 
materials must be moved, the quantity mixed at a time, etc. As a 
rough approximation it may be assumed that a common laborer can 
mix 3 yards per day, at a cost of, say, 50 cents per cubic yard. If 
the mixing is done by machinery, the cost may be as low as 25 
cents per cubic yard. The cost of a cubic yard of mortar composed 
of 1 part Portland cement and 2 parts sand, both by weight is 
then about as follows: 


Cement.2.80 bbls. (see page 88) @ $3.00 = $8.40 

Sand.0.78 cu. yd. (see page 88) .50 = .39 


Labor, handling materials and mixing.4 day @ $1.50 = .50 

Total cost of 1 cubic yard of mortar = $9.29 


* Compiled by Emil Iiuichling, for the report for 1888 of the Executive Board 
of the City of Rochester, N. Y. 









96 


MORTAR. 


[CHAP. IT- 


136. Natural vs. Portland Cement Mortar. It is sometimes a 
question whether Portland or natural cement should be used. If 
a quick-setting cement is required, then natural cement is to be 
preferred, since as a rule the natural cements are quicker setting, 
although there are many and marked exceptions to this rule. Other 
things being the same, a slow-setting cement is preferable, since 



Parts Sand to. I Part Cement by Weight 


Fig. 7a.—C ost of Cement Mortar. 

it is not so liable to set before reaching its place in the wall. This- 
is an important item, since with a quick-setting cement any slight 
delay may necessitate the throwing away of a boxful of mortar 
or the removal of a stone to scrape out the partially-set mortar. 

Generally, however, this question should be decided upon 
economical grounds, which makes it a question of relative strength 
and relative prices. The tensile strength of natural and'Portland 
cement mortars is shown in Fig. 6, page 92. The cost of mortar 
of various proportions of sand may be computed as in the preceding 
section; but as the cost of labor is uncertain and is substantially 
the same for both kinds of mortar, it is sufficient to deal with the 
cost of the materials only. Assuming Portland cement to cost $3 
per barrel, natural $1 per barrel, and sand 50 cents per cubic yard, 
and using Table 11, page 88, the cost of the materials in a cubic 
yard of mortar is as in Fig. 7 a. 



























ART. 1.] 


NATURAL YS. PORTLAND CEMENT MORTAR. 


97 



Cost of Mortar in Dollars per Cubic Yard 


Fig. 7 b . —Relative Economy op Natural and Portland Cements. 



Fig. 7c.—Economic Proportion of Sand. 




















































98 


MORTAR. 


[CHAP. IV.. 


By plotting the strength of Portland and natural cement mortar 
6 months old and the cost of a yard of mortar as given in Fig. 7 a. 
Fig. 75 is obtained, which shows the relation between the strength 
at 6 months and the cost of the mortar made of the two kinds of 
cement. Notice that for any tensile strength under about 370 
pounds per square inch, either natural or Portland cement may be 
used, but that the former is the cheaper. In other words, Fig. 75 
shows that if a strength of about 370 pounds per square inch at 
6 months is sufficient, natural cement is the cheaper. Nearly all 
carefully conducted tests of the strength of cement mortar 6 
months old or over give a similar result, except that the above 
limit is usually between 300 and 350 pounds. A considerable 
change in prices does not materially alter the result, and hence the 
conclusion may be drawn that if a strength of 300 to 350 pounds 
per square inch at 6 months is sufficient, natural cement is more 
economical than Portland. Incidentally Fig. 7c, page 97, shows 
the same relation. However, in this connection it should not be 
forgotten that other considerations than strength and cost may 
govern the choice of a cement; for example, uniformity of product, 
rapidity of set, and soundness are of equal or greater importance 
than strength and cost. 

Mortar made of two brands of Portland or natural cement will 
differ considerably in economic values, and hence to be of the 
highest value the above comparison should be made between the 
most economical Portland and the most economical natural cement 
as determined by the method described in § 111 h. 

Short-time tests do not warrant any general conclusion as to the 
relative economy of natural and Portland cements, since the 
strength at short times varies greatly with the activity of the 
cement. For example, the two upper diagrams of Fig. G, page 
92, when plotted as in Fig. 75 show Portland to be the more 
economical, while other similar experiments show natural cement to 
be the more economical. . . 

137. Economic Proportion of Sand. Fig. 7c, page 97, shows 
the ratio of strength to cost for different proportions of sand, for 
both Portland and natural cement; in other words, Fig. 7c shows 
the tensile strength in pounds per square inch for each dollar of the 
cost of a cubic yard of mortar. For example, if a natural cement 
mortar at G months has a tensile strength of 280 pounds per square 
inch, and costs $2.95 per yard, the strength per dollar is: 280 



ART. 1.] 


EFFECT OF RE-TEMPERING. 


99 


2.95 = 94.9 pounds per square inch. In this way Fig. 7 c was 
constructed, using the cost of mortar as given in Fig. 7 a and the 
strengtli as determined by L. C. Sabin in connection with the con¬ 
struction of the Poe lock on the St. Mary’s Falls Canal.* Accord¬ 
ing to this diagram the most economic mortar, either natural or 
Portland, consists of 3 parts sand to 1 part cement, by weight. 

A study of the results of other experiments shows that the above 
conclusions are not general. The maximum ratio as above is 
different for different ages for the same cement, and at the same 
age is different for different cements. The above ratio varies (1) 
with the activity of the cement, which determines the strength 
neat at different ages; (2) with the fineness, which determines the 
sand-carrying power of the cement; (3) with the fineness of the 
sand, which determines the surface to be covered by the cement; 
and (4) with the cost of the cement and the sand. If the strength 
of any particular cement with the various proportions of sand is 
known for a particular age, and the price of the cement and sand 
also is known, the most economic propertion of sand can be com¬ 
puted as above. To determine the most economic mortar, the 
most economic cement should be selected as described in § 111 h y 
and then be mixed with the most economical proportion of sand as 
above. 

Strictly, the maximum ratio of strength to cost determined as 
above is not necessarily the most economical mortar. The work in 
hand may not require a mortar as strong as that giving the maxi¬ 
mum ratio of strength to cost, in which case a mortar having a 
smaller proportion of cement may be used; and similarly, if the 
work requires a mortar stronger than that giving the maximum 
ratio of strength and cost, then a mortar must be used which con¬ 
tains a greater proportion of cement. 

138. Effect of Re-tempering. Frequently, in practice, 
cement mortar which has taken an initial set, is re-mixed and used. 
Masons generally claim that re-tempering, i.e., adding water and 
re-mixing, is beneficial; while engineers and architects usually 
specify that mortar which has taken an initial set shall not be used. 

Re-tempering makes the mortar slightly less “short” or 
“brash,” that is, a little more plastic and easy to handle. Re¬ 
tempering also increases the time of set, the increase being very 


* Report of Chief of Engineers, U. S. A., 1893, page 3019, Table 4. 





100 


MORTAR. 


[CHAP. IV. 


different for different cements. But on the other hand, re-temper¬ 
ing usually weakens a cement mortar. A quick-setting natural 
cement sometimes loses 30 or 40 per cent, of its strength by being 
re-tempered after standing 20 minutes, and 70 or 80 per cent, by 
being re-tempered after standing 1 hour. With slow-setting 
cements, particularly Portlands, the loss by re-tempering immedi¬ 
ately after initial set (§ 84) is not material. A mortar which has 
been insufficiently worked is sometimes made appreciably stronger 
by re-tempering, the additional labor in re-mixing more than com¬ 
pensating for the loss caused by breaking the set. 

The loss of strength by re-tempering is greater for quick-setting 
than for slow-setting cement, and greater for neat than for sand 
mortar, and greater with fine sand than with coarse. The loss 
increases with the amount of set. If mortar is to stand a consider¬ 
able time, the injury will be less if it is re-tempered several times 
during the interval than if it is allowed to stand undisturbed to the 
end of the time and is then re-mixed. Re-tempered mortar shrinks 
more in setting than ordinary mortar. This fact sometimes 
accounts for the cracks which frequently appear upon a troweled 
surface. 

The only safe rule for practical work is to require the mortar 
to be thoroughly mixed, and then not permit any to be used which 
has taken an initial set (§ 84). This rule should be more 
strenuously insisted upon with natural than with Portland cements, 
and more with quick-setting than with slow-setting varieties. 

139. Lime with Cement. Cement mortar before it begins to 
set has no cohesive or adhesive properties, and is what the mason 
calls “ poor,” “ short,” “ brash ”; and consequently is difficult to 
use. It will not stick to the edge of the brick or stone already laid 
sufficiently to give mortar with which to strike the joint. The 
addition of a small per cent, of lime paste makes the mortar “ fat ” 
or “ rich,” and more pleasant to work. The substitution of 10 to 
20 per cent, of lime paste for an equal volume of the cement paste 
does not materially decrease the strength of the mortar, and 
frequently the addition of this amount of lime slightly increases its 
strength. In all cases the substitution of 10 to 20 per cent, of lime 
decreases the cost more rapidly than the strength, and hence is 
economical; but the substitution of more than about 20 per cent, 
decreases the strength more rapidly than the cost, and hence is not 
economical. The economy of using lime with cement is, of course, 





ART. 1.] 


MORTAR IMPERVIOUS TO WATER. 


101 


greater with Portland than with natural cement owing to the 
greater cost of the former. 

If the mortar is porous, t.e., if the voids of the sand are not 
filled with cement, the addition of lime will make the mortar more 
dense and plastic, and will also increase its strength and cost. The 
increase in strength is not proportional to the increase in cost, but 
the increased plasticity and density justify the increased cost—the 
former adds to the ease of using the mortar, and the latter to its 
durability. 

The addition of lime does not materially affect the time of set, 
and usually slightly increases it. 

It has long been an American practice to reinforce lime mortar 
by the addition of hydraulic cement. The mortar for the 
“ordinary brickwork” of the United States public buildings is 
composed of “ one fourth cement, one half sand, and one fourth 
lime.” The cement adds somewhat to the strength of the mortar, 
but not proportionally to the increase in the cost of the mortar. 

140. Mortar Impervious to Water. Nearly every failure 
of masonry is due to the disintegration of the mortar in the outside 
of the joints. Ordinary mortar—either lime or cement—absorbs 
water freely, common lime mortar absorbing from 50 to 60 per cent, 
of its own weight, and the best Portland cement mortar from 10 
to 20 per cent.; and consequently they disintegrate under the 
action of frost. Mortar may be made practically non-absorbent 
by the addition of alum and potash soap. One per cent., by 
weight, of powdered alum is added to the dry cement and sand, and 
thoroughly mixed; and about one per cent, of any potash soap 
(ordinary soft-soap made from wood ashes is very good) is dissolved 
In the water used in making the mortar. The alum and soap com¬ 
bine, and form compounds of alumina and the fatty acids, which 
are insoluble in water. These compounds are not acted upon by 
the carbonic acid of the air, and add considerably to the early 
strength of the mortar, and somewhat to its ultimate strength. 

With lime mortar, the alum and soap has a slight disadvantage 
in that the compounds which render the mortar impervious to water 
also prevent the air from coming in contact with the lime, and 
consequently prevent the setting of the mortar. On the other 
hand, the alum and soap compounds add considerably to both the 
early and the ultimate strength of the mortar. 

This method of rendering mortar impervious is an application 





102 


MORTAR. 


[CHAP. IV~ 


of the principle of Sylvester’s method of repelling moisture from 
external walls by applying alnm and soap washes alternately on the 
outside of the wall (see g 263). The same principle is applied in 
McMurtrie’s artificial stone (see § 162). The alum and soap are 
easily used, and do not add greatly to the cost of the mortar. The 
mixture could be advantageously used in plastering, and in both 
cement and lime mortars of outside walls or masonry in damp 
places. It has been very successfully used in the plastering of 
cellar and basement walls. It should be employed in all mortar 
used for pointing (§ 204). 

The addition of a small amount of very finely powdered clay 
(§ 114c) decreases the permeability of mortar; but since clay absorbs 
and parts with water with the changing seasons, the use of clay is 
not efficient in preventing disintegration by freezing and thawing. 

141. Freezing of Mortar. The freezing of mortar before it 
has set lias two effects: (1) the low temperature retards the setting 
and hardening action; and (2) the expansive force of the freezing 
water tends to destroy the cohesive strength of the mortar. 

142. Effect on Lime Mortar. The freezing of lime mortar 
retards the evaporation of the water, and consequently delays the 
combination of the lime with the carbonic gas of the atmosphere. 
The expansive action of the freezing water is not very serious upon 
lime mortar, since it hardens so slowly. Consequently lime mortar 
is not seriously injured by freezing, provided it remains frozen 
until fully set. Alternate freezing and thawing somewhat damages 
its adhesive and cohesive strength. However, even if the strength 
of the mortar were not materially affected by freezing and thawing,, 
it is not permissible to lay masonry during freezing weather; for 
example, if the mortar in a thin wall freezes before setting and 
afterwards thaws on one side only, the wall may settle injuriously. 

When masonry is to be laid in lime mortar during freezing 
weather, frequently the mortar is mixed with a minimum of water 
and then thinned to the proper consistency by adding hot water 
just before using. This is undesirable practice (see § 118). When 
* the very best results are sought, the brick or stone should be 
warmed—enough to thaw off any ice upon the surface is sufficient 
—before being laid. They may be warmed either by laying them 
on a furnace, or by suspending them over a slow fire, or by wetting 
with hot water, or by blowing steam through a hose against them. 

143. Effect on Cement Mortar. Owing to the retardation of the 



ART. 1.] 


EFFECT OF FREEZING. 


103- 

low temperature, the setting and hardening may be so delayed that 
the water may be dried out of the mortar and not leave enough for 
the chemical action of hardening; and consequently the mortar will 
be weak and crumbly. This would-be substantially the same as 
using mortar with a dry porous brick. Whether the water evapo¬ 
rates to an injurious extent or not depends upon the humidity of 
the air, the temperature of the mortar, the activity of the cement, 
and the extent of the exposed surface of the mortar. The mortar 
in the interior of the wall is not likely to be injured by the loss of 
water while frozen; but the edges of the joints are often thus seri¬ 
ously injured. In the latter case the damage may be fully repaired 
by pointing the masonry (§ 204) after the mortar has fully set. 

On the other hand when the cement has partially set, if the 
expansive force of the freezing water is greater than the cohesive 
strength of the mortar, then the bond of the mortar is broken, and 
on thawing out the mortar will crumble. Whether this action will 
take place or not will depend chiefly upon the strength and activity 
of the cement, upon the amount of free water present, and upon 
the hardness at the time of freezing. The relative effects of these 
several elements is not known certainly; but it has been proven 
conclusively that for the best results the following precautions 
should be observed: 1. Use a quick-setting cement. 2. Make the 
mortar richer than for ordinary temperatures. 3. Use the mini¬ 
mum quantity of water in mixing the mortar. 4. Prevent freezing 
as long as possible. 

There are various ways of preventing freezing: 1. Cover the 
masonry with tarpaulin, straw, manure, etc. 2. Warm the stone 
and the ingredients of the mortar. Heating the ingredients is not 
of much advantage, particularly with Portland cement. 3. Instead 
of trying to maintain a temperature above the freezing point of 
fresh water, add salt to the water to prevent its freezing. The 
usual rule for adding salt is: “Dissolve 1 pound of salt in 18 
gallons of water when the temperature is at 32° Fahr., and add 
3 ounces of salt for every 3° of lower temperature.” The above 
rule gives a slight excess of salt. The following rule is scientifically 
correct and easier remembered: “ Add one per cent, of salt for each 
Fahrenheit degree below freezing.” Apparently salt slightly 
decreases the strength of cement mortar setting in air, and slightly 
increases the strength when setting in water.* 


* Report of Chief of Engineers, U. S. A., 1895, pp. 2963-74, 3015. 






104 


MORTAR. 


[CHAP. IV. 


Alternate freezing and thawing is more damaging than contin¬ 
uous freezing, since with the former the bond may be repeatedly 
broken; and the damage due to successive disturbance increases 
with the number. 

144. Practice has shown that Portland cement mortar of the 
usual proportions laid in the ordinary way is not materially injured 
by alternate freezing or thawing, or by a temperature of 10° to 
15° F. below freezing, except perhaps at the exposed edges of the 
joints. Under the same conditions natural cement mortar is liable 
to be materially damaged. 

By the use of salt, even in less proportions than specified above, 
or by warming the materials, masonry may be safely laid with 
Portland at a temperature of 0° F.; and the same may usually be 
done with natural cement, although it will ordinarily be necessary 
to re-point the masonry in the spring. Warming the materials is 
not as effective as using salt. 

145. Change of Volume in Setting. The Committee of the 
American Society of Civil Engineers draw the following conclu¬ 
sions:* 1. Cement mortars hardening in air diminish in linear 
dimensions, at least to the end of twelve weeks, and in most cases 
progressively. 2. Cement mortars hardening in water increase in 
like manner, but to a less degree. 3. The contractions and expan¬ 
sions are greatest in neat cement mortars. 4. The quick-setting 
cements show greater expansions and contractions than the slow- 
setting cements. 5. The changes are less in mortars containing 
sand. 6. The changes are less in water than in air. 7. The con¬ 
traction at the end of twelve weeks is as follows: for neat cement 
mortar, 0.14 to 0.32 per cent.; fora mortar composed of 1 part 
cement and 1 part sand, 0.08 to 0.17 per cent. 8. The expansion 
at the end of twelve weeks is as follows: for neat cement, 0.04 to 
0.25 per cent.; for 1 part cement and 1 part sand, 0.0 to 0.08 per 
cent. 9. The contraction or expansion is essentially the same in 
all directions. 

146. Elasticity, Compression, and Set of Mortar. For 

data on elasticity see page 14. The evidence is so conflicting that 
it is impossible to determine the coefficient of compression and of 

* See the “ Report of Progress of the Committee on the Compressive Strength of 
Cements and the Compression of Mortars and Settlement of Masonry,” in the 
Transactions of that Society, vol. xvii. pp. 213-37; also a similar report in vol. xvi. 
pp. 717-32. 





ART. 1.] ELASTICITY, COMPRESSION, AND SET OF MORTAR. 


105 


set of mortar, even approximately. For much valuable data on 
this and related subjects, see the “ Report of Progress of the Com¬ 
mittee on the Compressive Strength of Cements and the Compres¬ 
sion of Mortars and Settlement of Masonry,” in the Transactions of 
the American Society of Civil Engineers, vol. xvi. pp. 717-32, 
vol. xvii. pp. 213-17, and also vol. xviii. pp. 264-80. The several 
annual reports of tests made with the United States Government 
testing-machine at Watertown contain valuable data—particularly 
the report for 1884, pp. 69-247—bearing indirectly upon this and 
related subjects; but since some of the details of the experiments 
are wanting, and since the fundamental principles are not well 
enough understood to carry out intelligently a series of experiments, 
it is impossible to draw any valuable conclusions from the data. 


9 




# 



106 


CONCRETE. 


[CHAP. IV. 


Art. 2. Concrete. 

147. Concrete consists of mortar in which is embedded small 
pieces of some hard material. The mortar is often referred to as 
the matrix; and the embedded fragments, as the aggregate. Con¬ 
crete is a species of artificial stone. It is sometimes called beton, 
the French equivalent of concrete. 

“ Concrete is admirably adapted to a variety of most important 
uses. For foundations in damp and yielding soils and for subter¬ 
ranean and submarine masonry, under almost every combination of 
circumstances likely to be met with in practice, it is superior to 
brick masonry in strength, hardness, and durability; is more 
economical; and in some cases is a safe substitute for the best 
natural stone, while it is almost always preferable to the poorer 
varieties. For submarine masonry, concrete possesses the advan¬ 
tage that it can be laid, under certain precautions, without exhaust¬ 
ing the water and without the use of a diving-bell or submarine 
armor. On account of its continuity and its impermeability to 
water, it is an excellent material to form a substratum in soils 
infested with springs; for sewers and conduits; for basement and 
sustaining walls; for columns, piers, and abutments; for the 
hearting and backing of walls faced with.bricks, rubble, or ashlar 
work; for pavements in areas, basements, sidewalks, and cellars; 
for the walls and floors of cisterns, vaults, etc. Groined and 
vaulted arches, and even entire bridges, dwelling-houses, and fac¬ 
tories, in single monolithic masses, with suitable ornamentation, 
have been constructed of this material alone.” 

The great value of concrete in all kinds of foundations is slowly 
coming to be appreciated. It enables the engineer to build his 
superstructure on a monolith as long, as wide, and as deep as he 
may think best, which cannot fail in parts, but, if rightly propor¬ 
tioned, must go all together—if it fails at all. 

148. The Mortar. The matrix may be either lime or cement 
mortar, but is usually the latter. The term concrete is almost 
universally understood to be cement mortar with pebbles or broken 
stone embedded in it. Lime mortar is wholly unfit for use in large 
masses of concrete since it does not set when excluded from the air 
(see § 119). 



ART. 2.] 


THE AGGREGATE. 


107 


The cement mortar may be made as already described in Art. 1 
preceding. 

149. The Aggregate. The aggregate may consist of small 
pieces of any hard material, as pebbles, broken stone, broken brick, 
shells, slag, coke, etc. It is added to the mortar to reduce the 
cost, and within limits also adds to the strength of the concrete. 
Ordinarily either broken stone or gravel is used. Coke or blast¬ 
furnace slag is used when a light and not strong concrete is desired, 
as for the foundation of a pavement on a bridge or for the floors 
of a tall building. Of course a soft porous aggregate makes a weak 
concrete. 

Whatever the aggregate it should be free from dust, loam, or 
any weak material. The pieces should be of graduated sizes, so 
that the smaller shall fit into the voids between the larger. When 
this condition is satisfied less cement will be required and conse¬ 
quently the cost of the concrete will be less, and at the same time 
its strength will be greater. Other things being equal, the rougher 
the surfaces of the fragments the better the cement adheres, and 
consequently the stronger the concrete. 

150. It is sometimes specified that the broken stone to be used 
in making concrete shall be screened to practically an uniform size; 
but this is unwise for three reasons; viz.: 1. With graded sizes the 
smaller pieces fit into the spaces between the larger, and conse¬ 
quently less mortar is required to fill the spaces between the 
fragments of the stone. Therefore the unscreened broken stone is 
more economical than screened broken stone. 2. A concrete con¬ 
taining the smaller fragments of broken stone is stronger than 
though they were replaced with cement and sand. Experiments 
show that sandstone screenings give a considerably stronger mortar 
than natural sand of equal fineness, and that limestone screenings 
make stronger mortar than sandstone screenings, the latter giving 
from 10 to 50 per cent, stronger mortar than natural sand.* 
Hence, reasoning by analogy, we may conclude that including the 
finer particles of broken stone will make a stronger concrete than 
replacing them with mortar made of natural sand. Farther, 
experiments show that a concrete containing a considerable propor- 


* Annual Report of Chief of Engineers, U. S. A., 1893, Part 3, p. 3015; do. 1894, 
Part 4, p. 2321; do. 1895, Part 4, p. 2953; Jour. West. Soc. of Eng’rs, vol. ii. pp. 394 
and 400. 






108 


CONCRETE. 


[CHAP. IV.. 


tion of broken stone is stronger than the mortar alone (see the second 
and third paragraphs of § 153). Since the mortar alone is weaker 
than the concrete, the less the proportion of mortar the stronger the 
concrete, provided the voids of the aggregate are filled; and there¬ 
fore concrete made of broken stone of graded sizes is stronger than 
that made of practically one size of broken stone. 3. A single size 
of broken stone has a greater tendency to form arches while being 
rammed into place, than stone of graded sizes. 

Therefore concrete made with screened stone is more expensive 
and more liable to arch in being tamped into place, and is less dense 
and weaker than concrete made with unscreened stone. 

In short, screening the stone to nearly one size is not only a 
needless expense, but is also a positive detriment. 

The dust should be removed, since it has no strength of itself 
and adds greatly to the surface to be coated, and also prevents the 
contact of the cement and the body of the broken stone. Particles 
of the size of sand grains may be allowed to remain if not too fine 
nor in excess. The small particles of broken stone should be 
removed if to do so reduces the proportion of voids (§§ 115d, 115e). 

151. Gravel vs. Broken Stone. Often there is debate as to the 
relative merits of gravel and broken stone as the aggregate for con¬ 
crete ; but when compared upon the same basis there is no room for 
doubt. 

In the preceding section it was shown that finely crushed stone 
gave greater tensile and compressive strengths than equal propor¬ 
tions of sand; and hence reasoning by analogy, the conclusion is 
that concrete composed of broken stone is stronger than that con¬ 
taining an equal proportion of gravel. This element of strength is 
due to the fact that the cement adheres more closely to the rough 
surfaces of the angular fragments of broken stone than to the 
smooth surface of the rounded pebbles. 

Again, part of the resistance of concrete to crushing is due to 
the frictional resistance of one piece of aggregate to moving on 
another; and consequently for this reason broken stone is better 
than gravel. It is well known that broken stone makes better 
macadam than gravel, since the rounded pebbles are more easily 
displaced than the angular fragments of broken stone. Concrete 
differs from macadam only in the use of a better binding material; 
and the greater the frictional resistance between the particles the 
stronger the mass or the less the cement required. 




ART. 2.] 


THEORY OF THE PROPORTIONS. 


109 


A series of experiments* made by the City of Washington, 
D. C., to determine the relative value of broken stone and gravel 
for concrete, which are summarized in § 1575, page 112r, gives the 
following results: 

Strength of Gravel Concrete in terms of Broken Stone Concrete. 


Age of Concrete 


Concrete 

MADE WITH 

WHEN TESTED. 

Natural 

Cement. 

Portland Cement. 

10 days. 

38 per cent. 

76 per cent. 

45 “ 

78 “ 

< < 

91 “ “ 

3 months. 

96 “ 

< < 

119 “ “ 

6 “ 

43 “ 

<4 

73 “ “ 

1 year. 

83 “ 

C i 

108 “ “ 

Mean 

68 “ 

i < 

93 “ “ 


Each result is the mean for two 1-foot cubes, excejit that the values 
for a year are the means for five cubes. Notice that the gravel 
concrete is relatively weaker for the earlier ages, owing probably to 
the greater internal friction of the broken-stone concrete. 

In a series of forty-eight French experiments,! the crushing 
strength of gravel concrete with Portland cement is only 79 per 
cent, as great as that of broken-stone concrete. The gravel had 40 
per cent, of voids, while the broken stone had 47 per cent., which 
favored the gravel concrete (see § 154). The results of these tests 
are shown graphically in Fig. 8, page 112 a. 

152. Since frequently gravel is cheaper than broken stone, a 
mixture of broken stone and gravel may make a more efficient con¬ 
crete than either alone, i. e ., may give greater strength for the same 
cost, or give less cost for the same strength. 

153. Theory of the Proportions. The voids in the aggre¬ 
gate should always be filled with mortar. If there is not enough 
mortar to fill the voids, the concrete will be weak and porous. On 
the other hand, more mortar than enough to fill the voids of the 
aggregate increases the cost of the concrete and also decreases its 
strength. The decrease in strength due to an excess of mortar is 
usually greater than would be produced by substituting the same 
amount of aggregate, since ordinarily the sand and the aggregate 
have approximately the same per cent, of voids, while the sand has 
the greater, and also the smoother, surface. 


* Report of Engineer Commissioner of the District of Columbia for 1897, p. 1G5. 
f Cements et Chaux Hydrauliques, E. Candlot, Paris, 1891, pp. 215, and 340-41. 





110 


CONCRETE. 


[CHAP. IV. 


A correctly proportioned concrete is always stronger than the 
mortar alone. For example, Table 13 a * shows that a concrete 
containing a considerable proportion of pebbles is stronger than the 
mortar alone—compare lines 2, 5, and 8 with the preceding line of 
each group, respectively. The results are for gravel concrete, and 
they would be more striking for broken-stone concrete, since the 
cement adheres better to broken stone than to either sand or 
gravel. 

TABLE 13a. 

Relative Strength of Mortar and Gravel Concrete. 



Portland Cement. 

Tested when 28 Days old. 

Ref. No. 

Proportions. 


Strength of the 
Concrete in terms of 
that of the Mortar. 


Cement. 

Sand. 

Pebbles. 

Crushing Strength, 
lbs. per sq. in. 

1 

1 

2 

0 

2 158 

100 per cent. 

2 

% 


3 

2 783 

129 “ “ 

3 



5 

2 414 

126 “ “ 

4 

1 

3 

0 

1 406 

100 per cent. 

5 



5 

1 661 

114 “ “ 

6 



6.5 

1 534 

109 “ “ 

7 

1 

4 

0 

1 068 

100 per cent. 

8 


• 

5 

1 291 

121 “ “ 

9 



8.5 

1 221 

114 “ “ 


The average strength of twenty-four cubes ranging from 6 to 
16 inches on a side, made under the direction of Gen. Q. A. Gill- 
more,! and composed of 1 volume of cement, 3 volumes of sand, 
and 6 volumes of broken stone, was 15 per cent, more than that of 
corresponding cubes made of the mortar alone. In another series 
of the same experiments,]; the average strength of eight cubes of 

* Dr. R. Dycherhoff, a German authority, as quoted in “Der Portland Cement 
und seine Anwendungon im Bauwesen,” p. 90. 

f Notes on the Compressive Resistance of Freestones, Brick Piers, Hydraulic 
Cement, Mortar, and Concretes, Q. A. Gillmore. John Wiley & Sons, New York 
1888, pp. 137-40 and 143-46. 

1 Ibid., pp. 141-42. 

























ART. 2.] 


THEORY OF THE PROPORTIONS. 


Ill 


concrete composed of 1 part cement, 1^ parts sand, and 6 parts 
broken stone was 95 per cent, of that of corresponding cubes of the 
mortar alone, which is interesting as showing that a lean concrete 
is nearly as strong as a very rich mortar. 

A correctly proportioned concrete is also stronger than either a 
richer or a leaner mixture—see Table 13 i, page 112 A 

154. For the strongest and densest concrete, the voids of the 
aggregate should be filled with a rich strong mortar; but if a 
cheaper concrete is desired, fill the voids of the aggregate with sand 
and add as much cement as the cost will justify. In other words, 
to make a cheap concrete, use as lean a mortar as the circumstances 
warrant, but use enough of it to fill the voids of the aggregate. 
Sand is so cheap that there is no saving by omitting it; and the use 
of it makes the concrete more dense. 

The strength of a concrete varies nearly with the amount and 
strength of the cement used, provided the mortar is not more than 
enough to fill the voids. Table 13& shows the strength of con¬ 
crete in terms of the cement employed. The data from which 

TABLE 13A 


Relation between the Crushing Strength of Concrete and the 

Proportion of Cement. 

Mortar Equal to the Voids in the Aggregate. 


Ref. 

No. 

Composition of 
Moktar. 
Volumes Loose. 

Proportion of 
Cement. 

Crushing Strength, 

Pounds per Square Inch. 

Cement. 

Sand. 

Actual. 

Relative. 

Actual. 

Theoretical. 

Relative. 

1 

1 

1 

0.50 

1.00 

4,467 

5,000 

1.00 

2 

1 

2 

0.33 

0.67 

3,731 

3,300 

0.66 

3 

1 

3 

0.25 

0.50 

2,553 

2,500 

0.50 

4 

1 

4 

0.20 

0.40 

2,015 

2,000 

0.40 

5 

1 

5 

0.17 

0.33 

1,796 

1,600 

0.32 

6 

1 

6 

0.14 

0.28 

1,365 

1,400 

0.28 


this table was made are the same as those summarized in Table 
13/*, page 112y. The actual crushing strengths were plotted, and it 
was found that they could be reasonably well represented by a right 
line passing through the origin of co-ordinates. The values for this 
average line are shown in next to the last column of Table 13A 


























112a 


CONCRETE. 


[CHAP. IT. 


These experiments seem to prove that the strength of concrete 
varies as the quantity of cement, provided the voids are filled with 
mortar. The same conclusion is jiroved by the data summarized 



Fig. 8. —Relation between the Strength of the Concrete and the Amount of Cement. 

in Fig. 8. The diagram presents the results of forty-eight experi¬ 
ments on 4-incli cubes.* Each point represents two experiments, 
the age of the mortar in one being 7 days and in the other 28 days. 
The points with one circle around them represent the strength of 
broken-stone concrete, and the points with two circles gravel con¬ 
crete. Both the sand and the gravel employed in these experiments 
were very coarse, and consequently the amount of cement per cubic 
yard is unusually great. 

155. When mortar is mixed with broken stone, the film of 
mortar surrounding each fragment increases the volume of the 
resulting concrete. Table 13c, page 112£, gives the result of fifteen 
experiments to determine this increase in volume. The mortar was 


* Candlot’s Cements et Cliaux Ilydrauliques, pp. 340-41. 


























ART. 2.] 


THEORY OF THE PROPORTIONS. 


1126 


moderately dry, and the concrete was quite dry, moisture flushing 
to the surface only after vigorous tamping. The broken stone was 
No. 10 of Table 106, page 80, and contained 28 per cent, of voids 

i 

when rammed. 

Line 4 of Table 13c shows that if the mortar is equal to the 
voids, the volume of the rammed concrete is 7-J- per cent, more than 
the volume of the rammed broken stone alone. Possibly part of 

TABLE 13c. 


Increase of Volume by Mixing Mortar with Broken Stone. 


Ref. No. 

Volume of Mortar in 
terms of the Voids in 
the Broken Stone. * 

Volume of Rammed 
Concrete in terms of the 
Volume of Rammed 
Stone. 

Voids in the Rammed 
Concrete (while wet). 

1 

70 per cent. 

105.0 per cent. 

15.3 per cent. 

2 

80 “ 

105.5 “ “ 

12.2 “ 

3 

90 “ 

106.5 “ “ 

9.5 “ 

4 

100 “ “ 

107.5 “ “ 

7.0 “ 

5 

110 “ “ 

109.0 “ “ 

4.9 “ 

6 

120 “ “ 

110.5 “ 

2.8 “ “ 

7 

130 “ “ 

112.5 “ 

1.2 “ “ 

8 

140 “ 

114.0 “ “ 

0.0 “ 


the increase of volume was due to imperfect mixing, although it 
was believed that the mass was perfectly mixed. The table also 
shows that the voids in this concrete are equal to 7 per cent, of its 
volume; in other words, even though the volume of the mortar is 
equal to the volume of the voids, the voids are not filled. Appar¬ 
ently the voids can be entirely filled with this grade of mortar only 
when the mortar is about 40 per cent, in excess of the voids. 

The increase in volume in Table 13c may be regarded as the 
maximum, since the mortar was quite dry and the stone unscreened. 
With moderately wet mortar and the same stone, the increase in 
volume was only about half that in the table; and with moist 
mortar and stone ranging between 2 inches and 1 inch, there was 
no appreciable increase of volume. With pebbles the increase is 
only about two thirds that with broken stone of the same size. 
With fine gravel (No. 18, page 80) the per cent, of increase was 
considerably greater than in Table 13c; with mortar equal to 150 
per cent, of the voids, it was possible to fill only about 5 to 7 per 















112c 


CONCRETE. 


[CHAP. IV* 


cent, of the voids. The mortar used in Table 13c was 1 volume of 
cement to 2 volumes of sand, both measured loose; but with richer 
mortars the increase in volume was a little less, and wdth leaner 
mortars a little more. These differences are so small that they may 
be disregraded. 

Notice that the voids in Table 13c are for the wet concrete. 
When the concrete has dried out the voids will be more; since 
ordinarily all the water employed in making the concrete does not 
enter into chemical combination with the cement, and consequently 
when the concrete dries out the space occupied by the free water is 
empty. 

156. Methods of Determining the Proportions. There are two 
methods of fixing the proportions for a concrete; viz.: 1. adjust 
the proportions so that the voids of the aggregate shall be filled 
with mortar, and the voids of the sand with cement paste; or, 2, 
fix the proportions without reference to the voids in the materials. 
These two methods will be considered in order. 

15 6a. With Reference to the Voids. To find the correct pro¬ 
portions for a concrete, first determine the per cent, of voids in the 
rammed aggregate (§ 115c/). Next determine the voids in the 
sand. Then use that proportion of cement which will fill the voids 
of the sand with cement paste (see § 126). The amount of mortar 
to be used depends upon the per cent, of voids in the aggregate and 
the density desired in the concrete (see Table 13c, page 1125). 

The details of the method of determining the amount of mortar 
and of cement will be illustrated by the following example. Assume 
the aggregate to be broken stone, unscreened except to remove the 
dust, containing 28 per cent, of voids wdien rammed (see No. 10, 
Table 105, page 80). Also assume that a concrete of maximum 
density is desired; and that therefore the mortar should be equal 
to about 140 per cent, of the voids (see Table 13c, page 1125). The 
aggregate compacts 5 per cent, in ramming (No. 10, Table 105), 
and therefore a yard of loose material will equal 0.95 of a yard 
rammed. Adding mortar equal to 140 per cent, of the voids 
increases the volume to about 114 per cent. (Table 13c); and there¬ 
fore adding the mortar will increase the volume of the rammed 
aggregate to 0.95 X 1.14 = 1.08 cu. yd., which is the volume of 
concrete produced by a yard of loose aggregate. To produce a yard 
of concrete will therefore require 1 -f- 1.08 = 0.93 cn. yd. of loose 
broken stone. Since the mortar is to be equal to 140 per cent, of 



ART. 2.] METHODS OF DETERMINING THE PROPORTIONS. 


112 d 


the voids, a yard of concrete will require 1.40 X 0.28 = 0.39 cn. 
yd. of mortar. Assume the rammed sand to contain 37 per cent, 
of voids (see Table 10^, page 79 i). Therefore to fill the voids of 
the sand with cement paste will require 37 per cent, as much 
packed cement as loose sand; or in other words, the proportions of 
the mortar should be about 1 volume packed cement to 2-| volumes 
loose sand. Interpolating from Table 11, page 88, we see that to 
produce a yard of this mortar will require about 2.40 bbl. of Port¬ 
land cement and 0.79 cu. yd. of sand. Consequently a yard of the 
concrete will require 0.39 X 2.40 = 0.94 bbl. of Portland cement, 
and 0.39 X 0.79 = 0.31 cu. yd. of sand. The quantities for a 
cubic yard of the rammed concrete are: 0.94 bbl. of packed Port¬ 
land cement, 0.31 cn. yd. of loose sand, and 0.93 cu. yd. of loose 
broken stone; and since 1 bbl. = 0.13 cu. yd., the proportions 
are: 1 volume of packed Portland cement, 2^ volumes of loose 
sand, and 7-£ volumes of loose broken stone. 

156A Without Reference to the Voids. Usually the proportions 
of a concrete are fixed without any reference to the method to be 
employed in measuring the cement, and also without reference to 
the voids in the sand and in the aggregate. The proportions are 
usually stated in volumes, that of the cement being the unit. For 
example, a concrete is described as being 1 part cement, 2 parts 
sand, and 4 parts broken stone. 

This method is inexact, in the first place, since it does not state 
the degree of compactness of the cement. If the unit of cement is 
a commercial barrel of packed cement, the resulting concrete will 
be much richer than if the cement were measured loose (see § 126). 
In the second place, this method, in name and usually in fact, 
takes no account of the proportion of voids in either the sand or 
the aggregate. If the stone is screened to practically one size, it 
may have 45 to 50 per cent, of voids when rammed; but if it is 
unscreened except to remove the dust, it may have only 30 per 
cent, of voids (see Table 10 h, page 80). 

156c. To explain the method of testing whether or not the voids 
are filled in a concrete described in the above form, take the com¬ 
mon proportions: 1 volume cement, 2 volumes sand, and 4 volumes 
broken stone. If the cement is measured by volumes loose, as is 
usually the case, 1 volume of dry cement will make about 0.8 of a 
volume of paste. If the sand is the best, it will probably have 
about 30 per cent, of voids when rammed (see Table lOg, page 79 i) ■> 




112c 


CONCRETE. 


[CHAP. IV. 


and hence the 2 volumes of sand will contain about 0.6 of a volume 
of voids. The cement is then 25 per cent, more than enough to 
fill the voids of the sand. The cement and sand ’when rammed 
will make 2 + (0.8 — 0.6) = 2.2 -f- volumes of mortar.* If the 
broken stone is unscreened, it will probably have about 30 per cent, 
voids when rammed (see Table 10/*, page 80); and hence the 4 
volumes of stone will contain 1.2 volumes of voids. The excess of 
mortar is then 2.2 — 1.2 = 1.0 units, or 83 per cent, more than 
enough to fill the voids of the broken stone. The mortar and the 
broken stone will make 4 -f- (2.2 — 1.2) = 5.0 + volumes of 
rammed concrete.f 

For the materials assumed, the preceding proportions are very 
uneconomical, since there is 25 per cent, more cement than the 
voids in the sand and 83 per cent, more mortar than the voids in 
the broken stone. The possible saving in cement may be computed 
as follows: 25 per cent, of the cement could be omitted in making 
the mortar. The mortar would then be 2 volumes, of which 0.8 
of a volume, or 40 per cent., is in excess of the voids in the aggre¬ 
gate. The omission of this surplus mortar is equivalent to omitting 
0.40 x 0.75 = 30 per cent, of the original cement. The total 
surplus of cement is then 25 + 30 = 55 per cent. If the above 
proportions were intended to give a concrete of maximum density, 
then the mortar employed should be about 40 per cent, in excess 
of the void (§ 155). In this case, the surplus mortar would be 
(2.0 — 1.40 X 1.2) = 0.32 volumes, or 16 per cent, of the total 
mortar; and the surplus cement in this mortar would be (0.75x0.16) 
= 12 per cent. Therefore the total surplus cement is 25 -)- 12 — 
37 per cent. Even in this case the proportions are uneconomical. 

15 Qd. The above example shows how extravagant the above 
proportions are with the best grades of sand and broken stone. If 
the sand has 37-J per cent, of voids and the broken stone 40 per 
cent., then with the preceding proportions there will be practically 
no surplus cement, and there will be an excess of mortar of about 
25 per cent. In other words, with coarse sand and screened stone, 
the voids of the sand will be filled with cement paste, and the voids 

* The mortar when rammed will make from 2 to 4 per cent, more volume than, 
the sum of the sand and tho excess of the paste (see the last paragraph of § 128, 
page 87). 

+ The volume of the concrete will be slightly more than 5.0 units, since some 
sand will remain between the fragments of stone, and thereby increase the volume 
(see Table 13c, page 1125.) 






ART. 2.] 


DATA FOR ESTIMATES. 


112/ 


of the broken stone will be filled with mortar. However, it is 
exceedingly uneconomical to use a very porous aggregate and 
attempt to make a very dense concrete. 

The above comparisons show how unscientific it is to proportion 
concrete regardless of the condition of the materials to be used. 

156e. Occasionally specifications state the quality of the mortar 
to be used, and reqnire the mortar and the aggregate to be so pro¬ 
portioned that the mortar shall at least be equal to the voids in the 
aggregate. Under this method of procedure, to guard against lack 
of uniformity in the aggregate, imperfect mixing, and insufficient 
tamping, it is customary to require more than enough mortar to 
fill the voids, this excess varying from 0 to 50 per cent., but usually 
being from 15 to 25. Apparently 15 per cent, is frequently used 
in Germany.* 

Notice that this method is an approximation to that discussed 
in § 156a preceding. 

156/. Data for Estimates. Table 13 d and Table 13e, pages 
112# and 112/i, give the quantities of cement, sand, and broken stone 
required to make a cubic yard of concrete, for the two methods of 
proportioning described in § 156a and g 156&, respectively. Each 
table gives the quantities for unscreened and also for screened 
broken stone; and Table 13 cl gives also the quantities of cement 
and gravel required for a cubic yard of concrete. 

The barrel of cement in both tables is the commercial barrel of 
packed cement. 

156#. Table 13d is recommended for general use. The first line 
gives a concrete of the maximum density and maximum strength, 
i.e ., the quantity of mortar is sufficient to fill the voids (see § 155); 
and the successive lines give concretes of decreasing density and 
strength. The third and subsequent lines give concretes containing 
mortar equal to the voids, the mortar in the third line being 1 to 3, 
in the fourth 1 to 4, etc. 

The quantities were computed as described in § 156a, and were 
afterwards checked by making 8-inch cubes of concrete. While 
the results are only approximate for any particular case, it is 
believed that they represent average conditions with reasonable 

accuracy. 

The quantities in the table are for stone uniform in quality, and 


* Der Portland Cement und seine Anwendungen im Bauwesen, pp. 124 and 128. 






Ingredients required for a Cubic Yard of Rammed Concrete. 


112 g 


CONCRETE 


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CONCRETE. 


[CHAP. IV. 


11 2l 


for concrete thoroughly and vigorously rammed; and if it is desired 
certainly to secure the densest concrete, it might be wise to increase 
somewhat the cement and sand given in the first line of Table 13^. 
The per cent, of increase should vary with the circumstances of the 
case in hand (see § 156e). 

The proportions of the concretes can be determined by remem¬ 
bering that a barrel of cement is equal to 0.13 cu. yd. For example, 
for unscreened broken stone and Portland cement, the 0.94 bbl. of 
cement is equal to 0.12 cu. yd.; and the proportions are: 1 volume 
of packed cement, 2.5 volumes of loose sand, and 7.5 volumes of 
loose unscreened broken stone. If it be assumed that a barrel of 
packed cement will make 1.25 barrels when measured loose (see 
§ 126), the above proportions become: 1 volume loose cement, 
2.0 volumes loose sand, and 6.0 volumes loose unscreened broken 
stone. 

15Qh. Table 13e is given for use in determining the ingredients 
required for a concrete designed in the ordinary way—see § 156A 
The quantities were computed substantially as illustrated in 156c. 
This table is not as accurate as Table 13 d, and besides many of the 
proportions are uneconomical (see the second paragraph of § 156c). 

156/. Proportions from Practice. While a statement of the 
proportions used in practice may be of interest, it can not be of any 
great value since it is impracticable, if not impossible, to describe 
fully the circumstances and limitations under which the work was 
done. Farther the specifications and records from which such data 
must be drawn are frequently very indefinite. It is believed that 
the following examples are as accurate as it is possible or practicable 
to make them, and also that they are representative of the best 
American practice. 

For foundations for pavements: 1 volume of natural cement, 
2 volumes of sand, and 4 or 5, and occasionally 6, volumes of broken 
stone; or 1 volume of Portland cement, 3 volumes of sand, and 6 
or 7 volumes of broken stone. Occasionally gravel is specified, and 
more rarely gravel and broken stone mixed. 

For foundations and minor railroad work: 1 volume of natural 
cement, 2 volumes of sand, and 2 to 6, usually 4 or 5, parts of 
broken stone. See also pages 532 and 535. 

For important bridge and tunnel work: 1 part of Portland 
■cement, 3 parts of sand, and 4 or 5 parts of broken stone. 



ART. 2.] 


PROPORTIONS PROM PRACTICE. 


112/ 


For steel-grillage foundations: 1 part Portland cement, 1 part 
sand, and 2 parts broken stone. 

For the Melan steel and concrete construction the usual pro¬ 
portions are: 1 volume of Portland cement, 2-$- volumes of sand, 
5 volumes of broken stone. 

For the retaining walls on the Chicago Sanitary Canal: 1 part 
natural cement, 1 \ parts sand, and 4 parts unscreened limestone. 

For the dams, locks, etc., on the Illinois and Mississippi Canal: 
1 volume of loose Portland cement, 8 volumes of gravel and broken 
stone; or 1 volume loose natural cement and 5 volumes gravel and 
broken stone. 

For the Poe Lock of the St., Mary’s Fall Canal: 1 part natural 
cement, 1 % parts of sand, and 4 parts of sandstone broken to pass 
a 2-J-inch ring and not a f-inch screen. The broken stone had 46 
per cent, voids loose and 38 when rammed. 

In harbor improvements the proportions of concrete range from 
the richest (used to resist the violent action of waves and ice) to 
the very lowest (used for filling in cribwork). At Buffalo, N. Y., 
an extensive breakwater built in 1890 by the U. S. A. engineers, 
consisted of concrete blocks on the faces and a backing of concrete 
deposited in place. Portland was used for the blocks and natural 
for the backing, the proportions being: 1 volume cement, 3 sand, 
and 8-^ of broken stone and pebbles mixed in equal parts. 

For the concrete blocks used in constructing the Mississippi 
Jetties the proportions were: 1 part Portland cement, 1 part sand, 
1 part gravel, and 5 parts broken stone. 

For incidental information concerning proportions used in prac¬ 
tice, see Cost of Concrete, § 158$, page 112v. 

156/. Water Required. There is a considerable diversity of 
opinion among engineers as to the amount of water to be used in 
making concrete. According to one extreme, the amount of water 
should be such that the concrete will quake when tamped; or in 
other words, it should have the consistency of liver or jelly. 
According to the other extreme, the concrete should be mixed so 
dry that when thoroughly tamped moisture just flushes to the sur¬ 
face. The advocates of wet mixture claim that it makes the 
stronger and more dense concrete; while the advocates of dry mix¬ 
ture claim the opposite. The difference in practice is not as great 
as in theory; the apparent difference is chiefly due to differences 
in condition. 



112 k 


CONCRETE. 


[CHAP. IV. 


It is unquestionably true that dry mixtures of neat cement, and 
also of cement and sand, are stronger than wet mixtures, provided 
the amount of water is sufficient for the crystallization of the 
cement. It is also certainly true then in even a dry mortar or con¬ 
crete, the water is considerably in excess of that necessary for the 
crystallization of the cement, this excess increasing with the amount 
of sand and aggregate. Of course the excess water is an element 
of weakness. But the amount of water to be used in making con¬ 
crete is usually a question of expediency and cost, and not a ques¬ 
tion of the greatest attainable strength regardless of expense. 

1. Dry mixtures set more quickly and gain strength more 
rapidly than wet ones; and therefore if quick set and early strength 
are desired, dry concrete should be preferred. 2. Wet concrete 
contains a great number of invisible pores, while dry concrete is 
liable to contain a considerable number of visible voids; and for 
this reason there is liability that wet concrete will be pronounced 
the more dense, even though both have the same density. 3. Wet 
concrete is more easily mixed; and therefore if the concrete is mixed 
by hand and the supervision is insufficient or the labor is careless, 
or if the machine by which it is mixed is inefficient, wet mixtures 
are to be preferred. 4. Wet mixtures can be compacted into place 
with less effort than dry; but on the other hand the excess of water 
makes the mass more porous than though the concrete had been 
mixed dry and thoroughly compacted by ramming. Dry con¬ 
crete must be compacted by ramming, or it will be weak and 
porous; therefore if the concrete can not be rammed into place, it 
should be mixed wet and then the weight of the stones will bury 
themselves in the mortar, and the mortar will flow into the voids. 
5. A rich concrete can be compacted much easier than a lean one, 
owing to the lubricating effect of the mortar; a,nd hence rich con¬ 
cretes can be mixed dryer than lean ones. The quaking of concrete 
frequently is due more to an excess of mortar than to an excess of 
water. 6. Lean concretes should be mixed dry, since if wet the 
cement will find its way to the bottom of the layer and destroy the 
uniformity of the mixture. 7. Machine-made concrete may be 
mixed dryer than hand-made, owing to the more thorough incor¬ 
poration of the ingredients. 8. Gravel concrete can be more easily 
compacted than broken stone, and hence may be mixed dryer. 
Cement and sand alone is more easily compacted than when mixed 
with coarser material, particularly broken stone; and therefore 





ART. 2.J 


WATER REQUIRED. 


112? 


mortar to be deposited in mass should be mixed dryer than concrete. 

9. In mixing dry by hand there is a tendency for the cement to ball 
Tip, or form nodules of neat cement, while in mixing wet this does 
not occur. 10. If wet concrete is deposited in a wood form, there 
is liability of the water exuding between the planking and carrying 
away part of the cement and thus weakening the face—which should 
be the strongest part of the mass. 

The conclusion is that sometimes wet concrete must be used 
regardless of any question of strength and cost; while with thorough 
mixing and vigorous ramming, dry concrete is strongest but also 
most expensive to mix and lay. 

156 h. The following experiments are the only ones of any im¬ 
portance made to determine the relative strength of wet and dry 
concretes. The mean crushing strength of four hundred and 
ninety-six 1-foot cubes * made with mortar as “ dry as damp earth ” 
was 11 per cent, stronger than cubes made with mortar of the 
“ordinary consistency used by the average mason,” and 13 per 
cent, stronger than cubes that “ quaked like liver under moderate 
ramming.” The cubes were made of five brands of Portland 
cement, with broken stone and five proportions of sand varying 
from 1 to 1 to 1 to 5; half the cubes had a little more mortar than 
enough to fill the voids, while the other half had only about 80 per 
cent, as much mortar as voids. One quarter of the cubes were 
stored in water, one quarter in a cellar, one quarter under a wet 
cloth, and one quarter in the open air; and all were broken when 
approximately 2 years old. The difference in the amount of mortar 
made no appreciable difference in the strength. 

The mean of twelve cubes of dry concrete was 51 per cent, 
•stronger than corresponding cubes of quaking concrete.f 

A few minor experiments have been found confirming the above, * 
and none have been found that contradict them. 

156/. The amount of water required to produce any particular 
plasticity varies so greatly with the proportions of the ingredients, 
the kind and fineness of the cement, the dampness of the sand, the 
kind of aggregate, etc., that it is scarcely possible to give any valu¬ 
able general data. The water varies from 10 to 40 pounds per cubic 
foot of concrete. The only general rule that can be given is that for 

* Geo. W. Rafter, in Report of the New York State Engineer for 1897, pp. 375-460, 
particularly Table 4, page-398. 

f Foret, Engineering News, vol. xxvii, p. 311. 




112m 


CONCRETE. 


[CHAP. IV. 


dry concrete the aggregate should be wet but have no free water in 
the heap; and that the mortar should be damp enough to show 
water only when it is thoroughly rammed, or so that water will 
flush to the surface when it is tightly squeezed for a considerable 
time in the hand. 

In the experiments referred to in the first paragraph of the 
preceding section, the average quantity of water for the different 
grades of dry mortar was 19.8 lbs. per cu. ft., and for the plastic 
21.4, and for the wet 22.5, the sand being reasonably dry. 

156m. Mixing. —The value of the concrete depends greatly 
upon the thoroughness of the mixing. Every grain of sand and 
every fragment of aggregate should have cement adhering to every 
point of its surface. Thorough mixing should cause the cement 
not only to adhere to all the surfaces, hut should force it into 
intimate contact at every point. It is possible to increase the 
strength of really good concrete 100 per cent, by prolonged tritura¬ 
tion and rubbing together of its constituents. The longer and more 
thorough the mixing the better, provided the time does not trench 
upon the time of set or the working does not break and pulverize 
the angles of the stone. Uniformity of the mixture is as important 
as intimacy of contact between the ingredients. Of course thorough¬ 
ness of mixing adds to the cost, and it may be wiser to use more 
cement, or more concrete, and less labor. 

Concrete may be mixed by hand or by machinery. The latter 
is the better; since the work is more quickly and more thoroughly 
done, and since ordinarily the ingredients are brought into more 
intimate contact. Machine mixing is frequently specified. If any 
considerable quantity.is required, machine mixing is the cheaper, 
ordinarily costing only about half as much as hand mixing. 

156ft. Hand Mixing. The sand and aggregate are usually 
measured in wheelbarrows, the quantity being adjusted for a bag 
or barrel of cement. The dry cement and sand are mixed as 
described in the first paragraph of g 124 (page 85), which see. 
The proper quantity of water is then added, preferably with a 
spray to secure greater uniformity and prevent the washing away 
of the cement. The mass should be again turned until it is of 
uniform consistency. The broken stone, having previously been 
sprinkled but having no free water in the heap, is then added. The 
whole is then turned until every fragment is covered with cement. 
Specifications usually require concrete to be turned at least four 




ART. 2.] 


MIXING. 


112?? 


times, and frequently six. The concrete appears wetter each time 
it is turned, and should appear too dry until the very last. 

If gravel is used instead of broken stone, the mixing is done as 
described for cement and sand. 

156o. Machine Mixing. A variety of concrete-mixing machines 
are in use. Some forms are intermittent and some continuous in 
their action. Some of the latter automatically measure the in¬ 
gredients. A simple variety of the former consists of a cubical box 
revolved slowly about a diagonal axis. The dry materials are 
inserted through a door, and the water is admitted through the 
axis during the process of mixing. Eight or ten revolutions are 
sometimes specified; but eighteen or twenty are more frequently 
specified and give a much better concrete. Sometimes an inclined 
cylinder or long box revolving about the long axis is employed. 
Another form consists of a vertical box having a series of inclined 
shelves projecting alternately from opposite sides, the materials 
being thrown in at the top and becoming mixed by falling succes¬ 
sively from the inclined shelves. A modification of this form sub¬ 
stitutes rods for the shelves, the mixing being accomplished by the 
ingredients in their descent striking the rods. Still another type 
form consists of a spiral conveyor or a bladed screw-shaft revolving 
in a trough in which the materials are thrown. All of these forms, 
and also modifications of them, are to be had on the market. 

15 6y?. Laying. After mixing, the concrete is conveyed in wheel¬ 
barrows or in buckets swung from a crane, deposited in layers 6 to 
8 inches thick, and compacted by ramming. In dumping, the mass 
should not be allowed to fall from any considerable height, as doing 
so separates the ingredients. If in handling, the layer fragments 
become separated, they should be returned and be worked into the 
mass with the edge of a shovel. 

The rammer usually employed consists of a block of iron having 
a face 6 to 8 inches square and weighing anything up to 30 or 40 
pounds. The face of the rammer is sometimes corrugated, to keep 
the surface of the layer rough and thus afford a better bond with 
the next, and also to transfer the compacting effect of the blow to 
the bottom of the layer. The tamping should be vigorous enough 
to thoroughly compact the mass; but too severe or too long-con¬ 
tinued pounding injures the strength of the concrete by forcing the 
broken stone to the bottom of the layer, or by disturbing the 
incipient set of the cement. 




112o 


CONCRETE. 


[CHAP. IV. 


When one layer is laid on another already partially set, the 
entire surface of the latter should be thoroughly wet; but water 
should not stand in puddles. In case the first layer is fully set, it 
is wise to sweep the surface with neat cement paste to make sure 
that the two layers adhere firmly. If the sand or gravel contains 
any appreciable clay and the concrete is mixed wet, clay is liable to 
be flushed to the surface and prevent the adherence of the next 
layer; therefore under these conditions particular care should be 
given to secure a good union between the layers. After the con¬ 
crete is in place it should be protected from the sun, and not be 
disturbed by walking upon it until fully set: this limit should be 
at least 12 hours and is frequently specified as 4 or 5 days. 

156^. Depositing Concrete under Water. In laying concrete 
under water, an essential requisite is that the materials shall not 
fall from any height, but be deposited in the allotted place in a 
compact mass; otherwise the cement will be separated from the 
other ingredients and the strength of the work be seriously im¬ 
paired. If the concrete is allowed to fall through the water, its 
ingredients will be deposited in a series, the heaviest—the stone— 
at the bottom and the lightest—the cement—at the top, a fall of 
even a few feet causing an appreciable separation. Of course con¬ 
crete should not be used in running water, as the cement would be 
washed out. 

A common method of depositing concrete under water is to 
place it in a Y-shaped box of wood or plate-iron, which is lowered 
to the bottom by a crane. The box is so constructed that, on 
reaching the bottom, a pin may be drawn out by a string reaching 
to the surface, thus permitting one of the sloping sides to swing 
open and allowing the concrete to fall out. The box is then raised 
to be refilled. It usually has a lid. Concrete under water should 
not be rammed; but, if necessary, may be leveled by a rake or 
other suitable tool immediately after being deposited. 

A long box or tube, called a tremie , is also sometimes used. It 
consists of a tube open at top and bottom, built in detachable sec¬ 
tions so that the length may be adjusted to the depth of water. 
The tube is suspended from a crane, or movable frame running on a 
track, by which it is moved about as the work progresses. The 
upper end is hopper-shaped, and is kept above the water; the lower 
end rests against the bottom. The tremie is filled in the beginning 
by placing the lower end in a box with a movable bottom, filling 




ART. 2 ] 


STRENGTH. 


112 p 


the tube, lowering all to the bottom, and then detaching the 
bottom of the box. The tube is kept full of concrete, as the mass 
issues from the bottom more is thrown in at the top. 

Concrete has also been successfully deposited under water by 
enclosing it in paper bags, and lowering or sliding them down a 
chute into place. The bags get wet and the pressure of the con¬ 
crete soon bursts them, thus allowing the concrete to unite into a 
solid mass. Concrete is also sometimes deposited under water by 
enclosing it in open-clotli bags, the cement oozing through the 
meshes sufficiently to unite the whole into a single mass. 

When concrete is dejiosited in water, a pulpy gelatinous fluid is 
washed from the cement and rises to the surface. This causes the 
water to assume a milky hue; hence the term laitance , which 
French engineers apply to this substance. It is more abundant in 
salt water than in fresh water. It sets very slowly, and sometimes 
scarcely at all, and its interposition between the layers of concrete 
forms strata of separation. The proportion of laitance is greatly 
diminished by using large immersing boxes, or a tremie, or paper 
or cloth bags. 

157. Strength. The strength of concrete depends upon the 
kind and amount of cement, and upon the kind, size, and strength 
of the ballast. Mortar adheres to broken stone better than to 
pebbles, and therefore concrete containing the former is stronger 
than that containing the latter (see § 151). If the sizes of the indi¬ 
vidual pieces of the ballast are so adjusted that the smaller fit into 
the interstices of the larger, successively, then the cementing 
material will act to the best advantage and consequently the con¬ 
crete will be stronger. Hamming the concrete after it is in place 
brings the pieces of aggregate into closer contact, and consequently 
makes it stronger. The strength of concrete also depends somewhat 
upon the strength of the ballast, but chiefly upon the adhesion of 
the cement to the ballast. 

There are comparatively few experiments upon the strength 
of concrete in which the data was complete enough to make the 
results of any considerable value. 

157 a. Compressive Strength. In a series of experiments made 
by Geo. W. Rafter* to determine the crushing strength of concrete, 
three varieties of Portland cement were used, all of which were 


* Report of the New York State Engineer, 1897, pp. 375-460. 








112? 


CONCRETE. 


[CHAP. IT. 


equal to the maximum both neat and with sand in Table 10, page 
78a. The sand was pure, clean, sharp silica, containing 32 per 
cent, of voids. The aggregate was sandstone broken to pass a 
2-inch ring, having 37 per cent, voids when tamped. In half the 
blocks the mortar was a little more than enough to fill the voids; 
and in the other half the mortar was equal to about 80 per cent, of 
the voids. The mortar was mixed as “ dry as damp earth.” 

The test specimens were 1-foot cubes, and were stored under 
water for four months and then buried in sand. The age when 
tested ranged from 550 to G50 days, the average being about 600. 
The cubes were crushed on the U. S. Watertown Arsenal testing- 
machine. The means are shown in Table 13/. The individual 
results agreed well among themselves. 

TABLE 13/. 

Crusding Strength of Portland Concrete. 

Voids of broken stone practically filled with mortar—see the text. 

Age when tested 600 days. 


Ref. No. 

Composition 

of Mortar. 

No. 

of Cubes 
Tested. 

Crushing 

Strength. 

Cement. ' 

Sand. 

lbs. per sq. in. 

tons per sq. ft. 

1 

1 

1 

3 

4,467 

3.22 

2 

1 

2 

6 

3,731 

2.68 

3 

1 

3 

6 

2,553 

1.84 

4 

1 

4 

6 

2,015 

1.45 

5 

1 

5 

2 

1,796 

1.29 

6 

1 

6 

1 

1,365 

0.98 


The cubes summarized in Table 13/ were stored under water. 
Companion blocks stored in a cool cellar gave 82 per cent, as much 
strength; those fully exposed to the weather, 81 per cent.; and 
those covered with burlap and wetted several times a day for about 
three months and afterwards exposed to the weather, 80 per cent. 

The cubes of Table 13/ were mixed as “ dry as damp earth.” 
Companion blocks of which the mortar was mixed to the “ ordinary 
consistency used by the average mason,” gave 90 per cent, as much 
strength; and those mixed to “quake like liver under moderate 
ramming,” 88 per cent. 




















ART. 2.] 


COMPRESSIVE STRENGTH. 


112r 


157 b. Table 13 g shows the results of a series of experiments 
made by A. W. Dow, Inspector of Asphalt and Cement, Washing¬ 
ton, D. C.* 


TABLE 13<7. 


Crushing Strength of Concrete in Pounds per Square Inch. 


Ref. 

No. 

Composition of Concrete 
by Volumes Loose. 

Voids 

in Aggregate. 

Age of Cubes when Broken. 

Mortar. 

Aggregate in 
Sizes from 
2J4" to A". 

Per 

Cents. 

of 

volume 

Per 

Cent. 

of 

Voids 

filled 

with 

Mortar 

10 

Days. 

45 

Days. 

3 

Mos. 

6 

Mos. 

1 

Year. 

Cement 

Sand. 

Broken 

Stone. 

Gravel. 





Natural Cement. 






1 

1 

2 

6 

• ••••• 

45.3 

83.9 

228 

539 

375 

795 

915 

2 

1 

2 

6* 


45.7 

83.9 



596 


829 

3 

1 

2 

6f 


39.5 

96.2 





800 

4 

1 

2 

6 

29.3 

129.1 

87 

421 

361 

344 

763 

5 

1 

2 

3 

3 

35.5 

107.0 

108 

364 

593 

632 

841 

6 

1 

2 

4 

2 

37.8 

100.6 





915 



Port! 

and Ce 

ment. 






7 

1 

2 

6 

• ••••* 

45.3 

83.9 

908 

1,790 

2,260 

2,510 

3,060 

8 

1 

2 

6* 


45.7 

83.9 



1,630 

1,530 

1,850 

9 

1 

2 

6f 


39.5 

96.2 



2,700 

10 

1 

2 

6 

29.3 

129.1 

694 

1,630 

2,680 

1,840 

2,820 

11 

1 

2 

3 

3 

35.5 

107.0 

950 

1,850 


2,070 

2,750 

12 

1 

2 

4 

2 

37.8 

100.6 





2,840 


* Coarse. t Three fourths ordinary stone, one fourth granolithic. 


The strength of the cement is shown in Table 134. Notice that 
the Portland cement did not gain strength proportionally as fast as 
the natural cement; for example, the Portland mortar in line 7 is 
two and two-thirds times as strong as the preceding natural-cement 
mortar, while that in line 10 is not quite as strong as the natural- 
cement mortar immediately preceding. 


* Report of the Operations of the Engineering Department of the District of 
Columbia for the year ending June 30, 1897, pp. 160-66. 



























































1125 


CONCRETE. 


[CHAP. IV. 


TABLE 13/a. 


Tensile Strength of Cement used in Table 13 g . 


Ref. No. 

Age when Tested. 

Parts Standard 
Quartz to 1 part 
Cement. 

Tensile Strength, in. lbs. per sq. in. 

Natural. 

Portland. 

1 

1 day. 

0 

96 

441 

2 

7 days. 

0 

180 

839 

3 

7 “ 

2 

91 


4 

7 “ 

3 


248 

5 

1 mo. 

2 

188 


6 

1 “ 

3 


429 

7 

3 " 

2 

327 


8 

3 “ 

3 


398 

9 

6 “ 

2 

414 


10 

6 “ 

3 


428 

11 

1 vear. 

•/ 

2 

485 


12 

1 “ 

3 


474 


The fineness of the sand was as follows :* 0 3 75 G 7,5 8 13 10 30 20 32 
40 7 60 2 80 0,5 100 05 and contained 44.1 per cent, of voids. With 
the natural cement the water used was 0.317 cu. ft. (20 lbs.) per 
cn. ft. of rammed concrete, and with Portland cement 0.24 cu. ft. 
(12 lbs.)—in both cases including the moisture in the sand.f 

The broken stone was gneiss broken to pass a 2^-inch ring, none 
passing a No. 10 sieve, the voids for each particular concrete being 
as stated in Table 13 g. The gravel was clean quartz passing a 
1-J-inch ring and only 3 per cent, passing a No. 10 ring, and had 
29 per cent, of voids. The per cent, of voids in the aggregate filled 
with mortar is stated in Table 13 g. Each result in the table is the 
mean of two cubes, except those for one year, which are the mean 
of five. Owing to the friction of the press with which the tests 
were made, the results are 3 to 8 per cent, too high. 

157c. Table 13 j shows the relative strength of rich and lean 

*Eor explanation of the nomenclature, see the second paragraph of § 114e. 
t The sand contained 4.4 per cent, of water, which increased the volume of tho 
sand and made the mortar slightly richer than as stated. 


































ART. 2.] 


COMPRESSIVE STRENGTH. 


1 12f 


TABLE 13 i. 

Relative Strength of Rich and Lean Concretes. 



Proportions. 

Crushing Strength. 

Ref. No. 




One Week. 

Four Weeks. 




Broken 






Cement. 

Sand. 

Stone. 









Lbs. per 

Relative. 

Lbs. per 

Relative. 





sq. in. 


sq. in. 





Portlai 

id sand-c 

emeut 



1 

1 

H 

3 

412 

0.77 

490 

0.66 

2 



4 

446 

0.83 

679 

0.92 

3 



4.1 

536 

1.00 

741 

1.00 

4 

1 

2 

4 

316 

0.61 

441 

0.60 

5 



5 

275 

0.53 

477 

0.64 

6 



6 

521 

1.00 

639 

1.00 

7 

1 

3 

5 

144 

0.69 

274 

0.85 

8 



6 

110 

0.52 

182 

0.57 

9 



7 

210 

1.00 

322 

1.00 




English Portland 

cement 



10 

1 

2 

2 

494 

0.60 

565 

0.81 

11 



3 

611 

0.75 

555 

0.80 

12 



4 

819 

1.00 

613 

0.88 

13 



5 

581 

0.71 

680 

0.97 

14 



6 

500 

0.61 

698 

1.00 

15 

1 

3 

3 

333 


205 

0.53 

16 



4 



366 

0.95 

1 7 

a 


5 



386 

1.00 

1 ( 

18 ' 



6 



357 

0.92 



German 

Portland 

cement 



1 Q 

1 

2 

4 



626 

0.86 

20 

A 


5 



703 

0.97 

21 



6 



728 

1.00 





















































112 u 


CONCRETE. 


[CHAP. IV. 


concretes.* The water was equal to 20 per cent, of the weight of 
the cement and the sand. The test specimens for the Portland 
sand-cement were 9 inches square and 12 inches high, and for the 
remainder 12-inch cubes. All were crushed between sheets of rubber 
(see § 12, page 9). Each value in the table is the result for a single 
cube. Table 13 i is valuable chiefly as showing the relative strength 
of rich and lean concretes. The table shows that a moderately lean 
concrete is stronger than a very rich one, which is in accordance 
with the conclusion from Table 13 a, page 110, that a concrete is 
stronger than the mortar alone. Table 13t also shows that the 
strength of the concrete increases with the richness of the mortar, 
which agrees with Table 13page 111, and Fig. 8, page 112 a. 

157 d. For data on the crushing strength of gravel concrete, see 
Table 13«, page 110. 

For data on the crushing strength of gravel and broken-stone 
corncretes approximately 17 days old, see Fig. 8, page 112a. 

157e. The strength of concrete made of coke does not increase 
with age owing to the soft and friable nature of the aggregate. 
Apparently the maximum strength of 1 volume loose cement, 
3 volumes sand, and 5 volumes crushed coke is about GOO to 700 lbs. 
per sq. in. with Portland, and about 300 to 350 with natural cement. 

157/. Transverse Strength. Table 13 j, page 112i;, is a summary 
of 191 tests on concrete bars 30 inches long and 4 inches square/ 
The cement stood 497 lbs. per sq. in. neat at 7 days, and 209 lbs. 
with 3 parts sand at 4 weeks. In most of the bars the mortar was 
made of pulverized sandstone, although in some cases river and pit 
sands were used. The aggregate was generally broken sandstone, 
but gravel and broken whinstone were also used. “ In each case 
the voids in the 4 sand ’ were filled with cement, and those in the 
aggregate with mortar. ’ ’ 

The results are tabulated in the order of the ratio of the cement 
to the total sand and aggregate. Notice that the results in the last 
line are proportionally higher than those in the remainder of the 
table. This difference is probably due to the fact that the speci¬ 
mens for the first four lines were made with natural sand and 
stone, while in those for the last line only crushed sandstone was 
used for both the sand and the aggregate. 

* W. B. Anderson, Student Can. Soc. C. E., in Trans. Can. Soc. C. E., vol. xiii.. 
Part 1. 

f A. F. Bruce, in Proc. of Inst, of C. E. (London), vol. cxiii, pp. 217-28. 






ART. 2.] 


TRANSVERSE STRENGTH. 


HZv 


TABLE 13 j. 

Modulus of Rupture of Portland Concrete Bars, Pounds per 

Square Inch. 


Ref. 

No. 

Composition. 

Age in Weeks when Tested. 

Cement 

Sand. 

Aggre¬ 

gate. 

1 

4 

8 

12 

19 

26 

39 

1 

1 

2 

3 

95 

145 

215 

266 

301 

303 

320 

2 

1 


5 

37 

144 

165 

194 

268 

236 

259 

3 

1 

3 

5 


88 

129 

176 

191 

214 

214 

4 

1 

2 i 

6 

• « • • • • 

81 

130 

156 

193 

199 

212 

5 

1 

3 

7 

37 

113 

154 

187 

216 

243 

263 


157^. In connection with the construction of the Poe Lock of 
the St. Mary’s Falls Canal * a series of one hundred and forty-seven 
concrete beams 10 inches square were tested. The experiments 
were very carefully conducted, but there were so many variables 
that it is impossible to draw any general conclusions therefrom. 
The beams made with Portland cement were tested when about 19 
months old and those with natural cement when about 12 months. 

157 h. Weight of Concrete. The weight of concrete varies 
with the materials and the proportions, and with the amount of 
ramming. The weight varies from 130 to 160 lbs. per cu. ft., but 
is usually from 140 to 150. The difference in weight of the con¬ 
crete due to the aggregate and to the ramming is greater than that 
due to the difference in weight between Portland and natural 
cement. The maximum difference between Portland and natural 
concrete, due to the greater weight of Portland cement, is 4 or 
5 lbs. per cubic foot. Concrete made of blast-furnace slag weighs 
from 110 to 120 lbs. per cubic foot; and that made of coke from 
80 to 90 lbs. per cu. ft. 

158 a. Cost of Concrete. The cost of concrete varies greatly 
with the materials, the proportions, the cost of material and labor, 
etc. 

The following is the analysis of the composition and cost of the 
concrete employed for the foundations of the sea-wall at Lovell’s 
Island, Boston Harbor: f 

* Report of Chief of Engineers, U. S. A., 1895. Part 4, pp. 2922-31. 

f Compiled from Gillmore’s Limes, Hydraulic Cements and Mortars, p. 247. 

































112?# 


CONCRETE. 


[CHAP. IT, 


Cement, 0.83 bbl. 


@ $1 54 = 

$1 26 

Sand. 


@ 

70 

17 

Gravel. 


@ 

27 

24 

Total materials . 




$1 67 

Labor, making mortar. 


@ 

1 20 = 

08 

Labor, making concrete... 


@ 

1 20 

13 

Labor, transporting concrete.... 


@ 

1 20 

08 

Labor, packing concrete. 


@ 

1 20 

04 

Total labor . 




33 

Tools, implements, etc. 




11 

Total cost 1 cu. yd. of concrete, in place. . 



$2 11 


The proportions for this concrete were 1 cement, 3 sand, and 
4 gravel. It was unusually cheap, owing partly to the use of 
pebbles instead of broken stone. If the latter had been used, it 
would have cost probably 4 to 6 times as much as the gravel. The 
amount of labor required was also unusually small, this item alone 
being frequently 6 to 8 times as much as in this case. 

The following is the analysis * of the cost of nearly 10,000 yards 
of concrete as laid for the foundations of a blast-fnrnace plant near 
Troy, N. Y., in 1886. The conditions were unusually favorable 
for cheap work. The concrete consisted of 1 volume of packed 
cement to 7 of sand, gravel, and broken stone. 


Cement, 1.23 bbl. 


© $1 00 = $1 23 

Sand. 


@ 

0 30 = 03 

Gravel. 

. 0.36 “ 

@ 

0 30 = 11 

Broken stone. 


© 

1 41 = 1 04 

Total materials . 

. 1.38 “ 


. — $2 41 

Labor, handling cement. 


© 

1 00 = 02 

“ unloading stone. 

. 0.14 “ 

@ 

1 00 = 14 

“ mixing. 


@ 

1 00 = 85 

“ superintendence. 

. 0.01 “ 

© 

9 61 = 10 

Total labor .. 

. 1.02 “ 


— 1 09 

Total cost of a cubic yard of concrete, in place. 




* Trans. Am. Soc. of C. E., vol. xv. p. 875. 





















































ART. 2 .] 


COST OF CONCRETE. 


112 ar 


The following is the cost of the concrete used in the construc¬ 
tion of Hiland Avenue reservoir, Pittsburg, Penn.* The stone was 
broken so as to pass through a 2^-inch ring. The mortar was 
1 part Rosendale natural cement to 2 parts sand. The concrete 
was 1 part mortar to 2^ of stone. The concrete was mixed by hand. 
Common laborers received $1.25 per day, and foremen $2.50. The 
contract price was $6.00 per yard. 


Quarrying stone...$0 45 

Transporting stone. 50 

Breaking stone. 35 

Cement @ $1.35 per bbl.. 1 80 

Sand, cost of digging. 10 

Water. 05 

Labor, mixing and laying. 75 

Incidentals. 05 


Total cost per cubic yard, in place .$4 05 

The following is the cost of concrete in the foundations of an 
electric power-house at Pittsburg, Pa., in 1890.f The proportions 
were 1 volume of packed cement, 3 volumes of sand, and 5 volumes 
of broken stone. The cost of labor was abnormally high. The day 
was ten working hours. 


Portland cement 1.28 bbl. 


@$2.60 

$3.33 

Sand. 

. 0.50 “ 

@ 1.30 

0.65 

Broken stone. 

. 0.90 “ 

@ 1.25 

1.12 

Labor. 


@ 1.75 

1.59 

Superintendence. 

. 0.07 “ 

@ 3.00 

0.21 

Total cost per cu. yd.. 

in place .. 


.. $6 90 


The following is the cost of constructing the concrete retain¬ 
ing wall on the Chicago Sanitary Canal. J The average height of 
the wall was 10 ft. in Sec. 14, and 22 ft. in Sec. 15. The thickness 
on top was 6 ft., and at the bottom it was equal to half the height. 
The stone was taken from the adjacent canal excavation. The body 
of the wall was made with natural cement, but the coping and 
facing, each 3 inches thick, were made with Portland cement. 

* Emile Law in Engineei'ing Neics, vol. xiii. p. 51, 52. 

f E. T. Chibas in 'The Polytechnic, Rensselaer Polytechnic Institute, vol., vii. 
p. 145. 

X Jour. West. Soc. of Eng’rs, vol. iii. pp. 1310-32. 























11 % 


CONCRETE. 


[CHAP. IV. 


The proportions were 1 volume of cement, volumes of sand, and 
4 volumes of unscreened limestone. The cost of plant employed in 
Sec. 14 was $9,600, and in Sec. 15 was $25,420. The contract 
price for the concrete in Sec. 14 was $2.74, and in Sec. 15 $3.40 
per cu. yd. 


Items of Expense. 

Cost per 
Sec.14 

Cubic yard. 
Sec.15 

Labor, general.. 

. $0,078 

$0,082 

on the wall. 

. .108 

.116 

mixing concrete. 

. .121 

.250 

placing and removing forms. 

. .150 

.142 

transporting materials. . 

. .142 

.081 

quarrying stone. 

. .303 

.275 

crushing stone. 

. .073 

.128 

Total for labor . 

$0,975 

$1,074 

Material, cement, natural $0.65 per bbl. 

0.863 

.930 

“ Portland @ $2.25 “ “ 

.305 

.180 

sand.@ $1.35per cu. yd. .465 

.476 

Total for materials . 

. $1,633 

$1,586 

Machinery, cost of operating. 

. .407 

.567 

Total cost per cu. yd . 

$3,015 

$3,227 


For additional data concerning the cost of concrete, see 
§§ 233-34, page 157. 

158 b. The following items relate only to the labor of making 
concrete. 

Table 13& gives the details of the cost per cubic yard of the 
labor required in mixing and laying concrete for the Buffalo, N. Y., 
breakwater, constructed in 1887-89. The data were communicated 
by Capt. F. A. Mahan, Corps of Engineers, U. S. A., who had 
charge of the work. The total amount of concrete laid was 14,587 
cu. yds. The conditions under which the work was done varied 
considerably from year to year.* 

Table 13m gives the details of the labor required in mixing and 
laying concrete in the construction of the Boyd’s Corner dam.f 


* The work is fully described in Report of Chief of Engineers, U. S. A., for 1890, 
pp. 2808-35. 

f From an account of the construction of the Boyd’s Corner dam on the Croton 
River near New York City, by J. James R. Croes, in Trans. Am. Soc. of C. E., vol. 
ili. p. 360. 































ART. 2 .] 


COST OF CONCRETE. 


1122 : 


TABLE 13 k. 

Cost of Mixing and Laying Concrete. 



j 

Concrete mixed by 

Rep. 

No. 

Items. 

band. 

machinery. 



1888 

1887 

1889 

1 

Transporting cement from store-house. 

$0,078 

$0,128 

.26 

$0,098 

024 

2 

Measuring cement. 

3 

Mixing cement paste. 

[ .212 

.186 

.084 

4 

Measuring sand and pebbles. 

.172 

.285 

.116 

5 

Measuring broken stone.. 

.070 

.198 

.101 

6 

Mixing concrete. 

.557 

.152 

.103 

7 

Transporting concrete. 

.185 

.445 

.166 

8 

Spreading and ramming concrete. 

.270 

.502 

.392 

9 

Placing forms. 

.240 

.176 

.263 

10 

Building temporary railway... 



.181 






Total labor per cu. yd . 

$1,790 

$2,098 

$1,528 




TABLE 13m. 

Labor Required in Mixing and Laying Concrete. 


Labor per Cubic Yard. 


Kind of Labor. 

New York Storage Reservoir. 

St. Louis Reservoir. 

Mixed on level 
and wheeled in. 

Hoisted by 
steam and run 
on cars. 

All work on level 
—wheeled in. 

From 27 to 10 
feet below 
surface. 

From 10 be¬ 
low to 6 
above sur¬ 
face. 

From 6 to 28 
feet above 
surface. 

From 28 to 45 
feet above 
surface. 

Mixers—hand work, days. 

Derrick and car men, days. 

Engine, hours... 

j-0.223 

j-0.227 

0.145 

0.088 

0.152 

0.065 

0.127 

0.046 

0.071 

0.121 

0.070 

0.108 

0.071 

0.098 

0.035 

0.073 

0.603 

0.537 

0.399 

Handling sand, days. 

Handling stone, days. 

Carts, days. 

Ramming, days. 

j-0.161 

0.065 

0.125 

j- 0.114 

0.076 

0.078 

[-0.183 

0.088 

0.125 

[-0.134 

0.057 

0.107 

[0.250 

0.068 

0.128 



































































113a 


CONCRETE. 


[CHAP. IV. 


158c. The cost of mixing and laying 6 inches of concrete for a 
pavement foundation is about 7 cents per sq. yd., for 1 part cement, 
2 parts sand, and 4 parts broken stone, turned six times—exclusive 
of casting into place. With gravel instead of broken stone, the cost 
is about 6 cents per sq. yd.; and with four turnings instead of six, 
the cost is about half a cent less than the prices above. 

158 d. Economic Concrete. The relative economy of natural and 
Portland cement mortars can be investigated as explained in 
§§ 136, 137. 

The relative strengths of gravel and of broken-stone concretes 
are stated in the last two paragraphs of § 151. The relative 
economy of concrete made with broken stone and gravel will vary 
with the cost of each; but as a rule, when gravel costs less than 80 
per cent, of that of broken stone, gravel is more economical. 

The strengths of both broken-stone and gravel concretes are 
given in Table 13^, page 112r, for both natural and Portland 
cements at different ages. A studv of these results shows that the 
relative strength of natural and Portland concrete is different at 
different ages. For example, taking averages for 10 days, the 
Portland concrete was 6 times as strong as the natural concrete; 
while at a year the Portland concrete was only 3 times as strong as 
the natural concrete. At 45 days and also at G months, the Port¬ 
land concrete was 4 times stronger than the natural concrete; and 
at 3 months 5 times as strong. Taking averages for like dates 
and compositions, the Portland cement concrete was 3.7 times 
as strong as natural cement concrete. Since the proportions are 
the same in both, the relative cost of the two concretes will vary as 
the relative cost of a barrel of each kind of cement. Hence if the 
cost of a barrel of Portland cement is more than 3.7 times that of a 
barrel of natural, the latter is on the average the more economical; 
but if Portland cement costs ^ss than 3.7 times as much as the 
natural cement, then the former is on the average the more 
economical. Of course these relations would be different at different 
dates. 

158tf. The following example, from actual practice, illustrates 
the possibilities in the way of combinations between Portland and 
natural cements, and gravel and broken stone. The specifications 
called for a concrete composed of 1 volume of natural cement, 
2 volumes of sand, and 4 volumes of screened broken stone. The 
contractor found that at current prices a concrete composed of 
1 volume of Portland cement and 9 volumes of gravel would cost 


i 






ART. 3.] 


ARTIFICIAL STONE. 


1135 


about the same as the concrete specified. A test of the strength of 

the two concretes showed that at a week the Portland-gravel con¬ 
crete was 1.52 times as strong as the natural cement and broken- 
stone concrete; and at a month 1.59 times a3 strong. Therefore the 
Portland-gravel concrete was the more economical, and was used. 

Art. 3. Artificial Stone. 

159. Several kinds of artificial stone have come into use within 
the last twenty-five years for architectural and artistic purposes, and 
for the pavements of cellars, for footpaths, areas, and other locali¬ 
ties not subjected to the tread of heavy animals. They are all a 
combination of hydraulic cement and sand, pebbles, etc. Some of 
them possess very considerable merit, and are of value in districts 
where durable and cheap building-stone is not supplied by nature. 

The strength and hardness of all varieties of artificial stone vary 
directly with the ultimate strength and hardness attainable by the 
hydraulic ingredients employed. An obvious means of improving 
the quality of the stone, therefore, is the employment of the highest 
grades of cement. 

160. BETON-COIGNET. As made by its inventor, Coignet, of 
Paris, its usual ingredients are: Portland cement, siliceous hydraulic 
lime (like that obtained at Teil, France), and clean sand, mixed 
together with a little fresh water. The proportions are varied con¬ 
siderably for different kinds of work. The dry ingredients are first 
thoroughly mixed by hand, and again in a mill after moistening 
them very slightly with clean water. Moulds are then filled with 
the mixture, which is compacted by ramming. The peculiarities 
of this stone result from (1) the small quantity of water used in its 
manufacture, (2) a judicious choice of the qualities and proportions 
of the ingredients, and (3) the thoroughness with which the mixing 
is done. It is nothing more than hydraulic concrete, from which 
the coarse fragments have been omitted, and upon which have been 
conferred all the advantages to be derived from their thorough 
manipulation. It is used in France to a considerable extent in 
constructing the walls of houses, and in repairing masonry,—as 
bridge piers, culverts, etc. 

In this country a mixture of either natural or Portland cement 
and sand is frequently, but improperly, called Beton-Coignet. 

161. Portland Stone. This is a mixture of Portland cement 
and sand, or sand and gravel, compacted into form by tamping. 




114 


ARTIFICIAL STONE. 


[chap. IV. 


When properly made it possesses the essential requisites of strength 
and hardness in a degree proportionate to the value of the cement 
employed. The proportions of 1 measure of dry cement to 2 or 21- 
measures of sand will answer for most purposes. The manipulation 
should be prolonged and thorough to insure the production of a 
homogeneous stone. It is much used for flagging, for which pur¬ 
pose the surface layer, to the thickness of about half an inch, may 
advantageously be composed of 1 measure of cement to 1|- or 14 of 
sand. 

162. McMurtrie Stone. This stone consists essentially of the 
Portland stone described above, in the pores of which are formed 
compounds of alumina with the fatty acids by the double decom¬ 
position of alum and a potash soap (see § 140, page 101). These 
compounds are insoluble in water, are not acted upon by the car¬ 
bonic acid of the air, and add considerably to the early strength of 
the stone and somewhat to its ultimate strength. 

The peculiar merit of this stone is that its power of absorbing 
water is decreased by the use of the alum and the soap. All mor¬ 
tars and most of the artificial stones absorb water freely,—porous 
mortar from 50 to 60 per cent, of its own weight and the best Port¬ 
land from 10 to 20 per cent.,—and consequently they disintegrate 
rapidly under the action of frost. The absorbed water also dissolves 
the salts of magnesia, lime, soda, and potash (of all of which there 
is always more or less in cement), and on evaporating leaves a white 
efflorescence on the surface, which injures the appearance of the 
wall. For these reasons the ordinary artificial stones a*re in dis¬ 
repute for architectural purposes. The absorptive power of the Mc¬ 
Murtrie stone is about twice that of granite, about equal to that of 
the best limestones, and about one tenth or less of that of the best 
sandstones. It has been used in Washington, D. C., to a limited 
extent, the window trimmings of the National Museum and also the 
fronts of a few stores and dwellings being of this stone. It appears 
to have given entire satisfaction. 

163. Frear Stone. This is composed of siliceous sand and good 
Portland cement, to which gum shellac is added. The composition 
used by the inventor was 1 measure of cement and 2^- measures of 
sand moistened with an alkaline solution of shellac of sufficient 
strength to furnish an ounce of the shellac to a cubic foot of stone, 
d he shellac adds to the early strength of the stone \ but it is not 
certain that it adds to the ultimate strength, nor is it certain that 



ART. 3.] 


SOREL STONE. 


115 


the shellac may not decay and ultimately prove an element of 
weakness. 

When mixed, it is rammed into wooden moulds, and after setting 
is laid away to season,—which requires several months for best 
results. It was much used in architectural work in the West a few 
years ago, but did not give satisfaction. 

164. Ransome Stone. This is made by forming in the in¬ 
terstices of sand, gravel, or any pulverized stone a hard and 
insoluble cementing substance, by the natural decomposition of 
two chemical compounds in solution. Sand and the silicate of 
soda are mixed in the proportion of a gallon of the latter to a 
bushel of the former and rammed into moulds, or it may be 
rolled into slabs for footpaths, etc. At this stage of the process 
the blocks or slabs may be easily cut into any desired form. They 
are then immersed, under pressure, in a hot solution of chloride of 
calcium, after which they are thoroughly drenched with cold water 
—for a longer or shorter period, according to their size—to wash 
out the chloride of sodium formed during the operation. In 
England grindstones are frequently made by this process. 

165. SOREL Stone. Some years ago, M. Sorel, a French chemist, 
discovered that the oxychloride of magnesium possessed hydraulic 
energy in a remarkable degree. This cement is the basis of the 
Sorel stone. It is formed by adding a solution of chloride of mag¬ 
nesium, of the proper strength and in the proper proportions, to 
the oxide of magnesium. The strength of this stone, as well as its 
hardness, exceeds that of any other artificial stone yet produced, 
and may, when desirable, be made equal to that of the natural 
stone which furnishes the powder or sand used in its fabrication- 
The process is patented, and is used mainly in making emery-wheels. 
By incorporating large pebbles and cobble-stones in the mixture 
the stone can be made quite cheaply, and is therefore suitable for 
foundations and plain massive walls. 



CHAPTER V. 


QUARRYING. 

166. This is so large a subject that it cannot be more than en¬ 
tered upon here ; for greater detail, see treatises on Quarrying, Rock¬ 
blasting, and Tunneling. 

167. Sources of Building Stones. The bowlders, which are 
scattered promiscuously over the surface of the ground and also 
frequently buried in it, furnish an excellent building stone for massive 
structures where strength is essential. They are usually of tough 
granite or of a slaty structure, and are difficult to work. Sometimes 
they have a cleavage plane or rift, along which they may be split. 
They can be broken into irregular pieces by building a fire about 
them, and drenching them while hot with water, or they may be 
broken by explosives. 

Of course by far the greater quantity of stone is taken directly 
from quarries. All building-stone deposits have usually a certain 
amount of covering, consisting either of a portion of the same de¬ 
posit, which has been disintegrated by atmospheric influences, or of a 
later deposit. This covering is called the “cap-rock” or “strip¬ 
ping.” In opening the quarry, the solid portions of cap-rock are 
broken up by blasting, and the whole is carted out of the way. After 
a sufficient space is stripped, the next step necessary, when the quarry 
rock does not stand out in cliffs, is to excavate a narrow space on 
one side for a quarry face, either by blasting or by some of the 
methods to be described presently. 

168. Methods of Quarrying. After a considerable area has 
thus been laid bare, the stone is quarried in one of three ways. 

169. I . By Hand Tools. When the stone is thin-bedded, it may 
be quarried by hand-tools alone. The principal tools are pick, crow¬ 
bar, drill, hammer, wedge, and plug and feathers. The layers are 
forced apart by the crow-bar or wedges. The flat pieces are broken 
up with the hammer or by drilling holes for the plug and feathers. 

116 



QUARRYING BY EXPLOSIVES. 


117 


The plug is a narrow wedge with plane faces; the feathers are 
wedges flat on one side and rounded on the other (Fig. 25, page 128). 
When a plug is placed between two feathers, the three will slip into 
a cylindrical hole ; if the plug is then driven, it exerts a great force. 
If these plugs and feathers are placed a few inches apart in a row, 
and all driven at the same time, the stone will be cracked along the 
line of the holes, even though it be comparatively thick. 

The drill used to cut the holes for the plug and feathers is a bar 
of steel furnished with a wide edge sharpened to a blunt angle and 
hardened. It is operated by one man, who holds the drill with one 
hand and drives it with a hammer in the other, rotating the drill 
between blows. The holes are usually from f to f of an inch in 
diameter. 

Sandstones and limestones occurring in layers thin enough to 
be quarried as above are usually of inferior quality, suitable only 
for slope walls, paving, riprap, concrete, etc. 

170. II. By Explosives. Generally, the cheapest method of 
quarrying small blocks is by the use of explosives. However, ex¬ 
plosives are used mainly for detaching large blocks, which are after¬ 
wards worked up by means of wedges. In this method of quarry¬ 
ing, drill-boles are put down to the depth to which the rock is to 
be split, and the requisite amount of powder or other explosive put 
in, covered with sand, and fired by a fuse. Sometimes numerous 
charges in a line of drill-holes are fired simultaneously by means of 
electricitv. 

Quick-acting explosives, like dynamite, have a tendency to shatter 
the stone and break it in many directions, the texture being affected 
by the sudden explosion in the same manner as by the blow of a 
hammer. Coarse gunpowder is generally preferred for quarrying 
stone. Light charges of powder lightly covered with sand are better 
than heavy charges tightly tamped ; * and experience goes to show 
that better work is done by repeated light blasts in the same hole, 
than by a single heavy blast. By means of light charges often re¬ 
peated, a mass of rock may be detached without being broken up, 
which would be badly shattered by a single charge strong enough to 
detach it. 

In each locality the structure of the rock must be carefully 

* For an article showing that an air-space should be left between the explosive 
^and the tamping, see Engineering News, vol. xviii. p. 332. 










118 


QUARRYING. 


[CHAP. V, 


studied with a view to take advantage of the cleavage planes and 
natural joints. For quarrying each class of rocks there is a charac¬ 
teristic method employed, which is, however, varied in detail in 
different quarries. The minor details of quarry* methods are as;, 
various as the differences existing in the textures, structures, 
and modes of occurrence of the rocks quarried. Much depends 
upon how the blast is made. The direction in which the rock is 
most liable to break depends upon the structure of the rock and 
the shape of the drill-hole. Even such an apparently unimportant 
matter as the form of the bottom of the drill-hole into which the 
explosive is put has a very marked effect. If bored with a hand- 
drill, the hole is generally triangular at the bottom, and a blast in 
such a hole will break the rock in three directions. In some quar¬ 
ries the lines of fracture are made to follow predetermined directions 
by putting the charge of powder into canisters of special forms.* 
171. Drills. The holes are bored by jumpers, churn-drills, or 
machine-drills. The first is a drill similar to the one used for drill¬ 
ing holes for plugs and feathers (§ 169), except that it is larger and 
longer. It is usually held by one man, who rotates it between the- 

alternating blows from hammers in the hands of two other men.. 

• % 

Churn-drills are long, heavy drills, usually 6 to 8 feet in length. 
They are raised by the workmen, let fall, caught on the rebound, 
raised and rotated a little, and then dropped again, thus cutting 
a hole without being driven by the hammer. They are more eco¬ 
nomical than jumpers, especially for deep holes, as they cut faster 
and make larger holes than hand-drills. 

! 172. Machine rock-drills bore much more rapidly than hand- 
drills, and also more economically, provided the work is of sufficient, 
magnitude to justify the preliminary outlay. They drill in any 
direction, and can often be used in boring holes so located that they 
could not be bored by hand. They are worked either by steam 
directly, or by air compressed by steam or water-power and stored 
in a tank called a receiver and thence led to the drills through iron 
pipes. 

A variety of rock-drilling machines has been invented, f but, 
they can be grouped in two classes, viz., percussion-drills and rotat¬ 
ing drills. The method of action of the percussion-drill is the same 

* See Report on Quarry Industry in Vol. X. of the 10th Census, pp. 33, 34. 

t For a full account of the more important ones, see Drinker’s “ Tunneling.” 





QUARRYING BY EXPLOSIVES. 


119 


as that of the churn-drill already described. The usual form is 
that of a cylinder, in which a piston is moved by steam or com¬ 
pressed air, and the drill is attached to this piston so as to make a 
stroke with every complete movement of the piston. An automatic 
device causes it to rotate slightly at each stroke. 

173. In the rotating drills, the drill-rod is a long tube, revolving 
about its axis. The end of the tube—hardened so as to form an 
annular cutting edge—is kept in contact with the rock, and by its 
rotation cuts in it a cylindrical hole, generally with a solid core in 
the center. The drill-rod is fed forward, or into the hole, as the 
drilling proceeds. The debris is removed from the hole by a con¬ 
stant stream of water which is forced to the bottom of the hole 
through the hollow drill-rod, and which carries the debris up 
through the narrow space between the outside of the drill-rod and 
the sides of the hole. 

The diamond drill is the only form of rotary rock-drill exten¬ 
sively used in this country. The tube has a head at its lower end, 
in which are set a number of carbons or black diamonds. The 
diamonds usually project slightly beyond the circumference of the 
head, which is perforated to permit the ingress and egress of the 
water used in removing the debris from the hole and at the same 
time prevent the head from binding in the hole. When it is desir¬ 
able to know the precise nature and stratification of the rock pene¬ 
trated, the cutting points are so arranged as to cut an annular groove 
in the rock, leaving a solid core, which is broken off: and lifted out 
whenever the head is brought up. "W here it is not desired to pre¬ 
serve the core intact, a solid boring-bit is used instead of the core¬ 
bit. They are made of any size up to 15 inches in diameter. 

174. Explosives * The principal explosives are gunpowder, 
nitro-glycerine, and dynamite. Only a coarse-grained and cheap 
variety of the first is used in quarrying, the others being too sudden 
and too strong in their action. 

The pressure exerted by gunpowder when fired in a confined 
space depends upon the relative weight and quality of powder used, 
and upon the space occupied by the gases evolved. The absolute 
force of gunpowder, the force which it exerts when it exactly fills 
the space in which it is confined, has never been satisfactorily ascer- 

* For a full account of all the various explosives, see Drinker’s “ Tunneling,” 
and Drinker’s “ Modern Explosives.” 






120 


QUARRYING. 


[CHAP. V. 


tained. It has been variously estimated at from 15,000 to 1,500,000 
pounds per square inch. Experiments by Gen. Rodman show that 
for the powder used in gunnery the absolute force of explosion is 
at least 200,000 pounds per square inch. “ In ordinary quarrying,, 
a cubic yard of solid rock in place (or about 1.9 cubic yards piled 
up after being quarried) requires from \ to f pound of powder. 
In very refractory rock, lying badly for quarrying, a solid yard may 
require from 1 to 2 pounds. In some of the most successful great- 
blasts for the Holyhead Breakwater, Wales, (where several thou¬ 
sands of pounds of powder were exploded, usually by galvanism, at 
a single shot,) from 2 to 4 cubic yards (solid) were loosened per 
pound of powder ; but in mai^ instances not more than 1 to 1£ 
yards. Tunnels and shafts require 2 to 6 pounds per solid yard, 
usually 3 to 5 pounds. Soft, partially decomposed rock frequently 
requires more than harder ones.” * 

The explosion of the powder splits and loosens a mass of rock 
whose volume is approximately proportional to the cube of the line 
of least resistance ,—that is, of the shortest distance from the charge 
to the surface of the rock,—and may be roughly estimated at twice 
that cube ; but this proportion varies much in different cases. The 
ordinary rule for the weight of powder in small blasts is 

Powder, in pounds, — (Line of Resistance, in feetff -r- 32. 

Powder is sold in kegs of 25 lbs., costing about $2.00 to $2.25 
per keg, exclusive of freight,—which is very high, owing to the risk. 

175. Most of the explosives which of late years have been tak¬ 
ing the place of gunpowder consist of a powdered substance, partly 
saturated with nitro-glycerine—a fluid produced by mixing glycerine 
with nitric and sulphuric acids. Nitro-glycerine, and the powders 
containing it, are always exploded by means of sharp percussion, 
which is applied by means of a cap and fuse. The cap is a hollow 
copper cylinder, about J inch in diameter and an inch or two in 
length, containing a cement composed of fulminate of mercury and 
some inert substance. The cap is called single-force, double-force, 
etc., according to the amount of explosive it contains. 

The principal advantages of nitro-glycerine as an explosive con¬ 
sist (1) in its instantaneous development of force, due to the fact 
that, pound for pound, it produces at least three and a half times. 


* Trautwine’s Engineer’s Pocket-book. 






QUARRYING BY EXPLOSIVES. 


121 


as much gas, and twice as much heat, as gunpowder ; and (2) in its 
high specific gravity, which permits the use of small drill-holes. 

Nitro-glycerine is rarely used in the liquid state in ordinary 
quarrying or blasting, owing to the liability of explosion through 
accidental percussion, and owing to its liability to leakage. It ex¬ 
plodes so suddenly that very little tamping is required, the mere 
weight of moist sand, earth, or water being sufficient. This fact, 
and the additional one that nitro-glycerine is unaffected by immer¬ 
sion in water and is heavier than water, render it particularly suit¬ 
able for sub-aqueous work, or for holes containing water. If the 
rock is seamy, the nitro-glycerine must be confined in water-tight 
casings. Such casings, however, necessarily leave some spaces be¬ 
tween the rock and the explosive, which diminishes the effect of the 
latter. The liquid condition of nitro-glycerine is useful in causing 
it to fill the drill-hole completely, so that there are no empty spaces 
in it to waste the force of the explosion. On the other hand, the 
liquid form is a disadvantage, because when thus used in seamy 
rock without a containing vessel portions of the nitro-glycerine leak 
away and remain unexploded and unsuspected, and may cause acci¬ 
dental explosion at a future time. 

The price of nitro-glycerine is from 50 to 60 cents per quart. 

176. Dynamite is the name given to any explosive which con¬ 
tains nitro-glycerine mixed with a granular absorbent. If the 
absorbent is inert, the mixture is called true dynamite; if the 
absorbent itself contains explosive substances, the mixture is called 
false dynamite. The absorbent, by its granular and compressible 
condition, acts as a cushion to the nitro-glycerine, and protects it 
from percussion and from the consequent danger of explosion, but 
does not diminish its power when exploded. Nitro-glycerine 
undergoes no change in composition by being absorbed ; and it 
then freezes, burns, explodes, etc., under the same conditions as 
to pressure, temperature, etc., as when in the liquid form. The 
cushioning effect of the absorbent merely renders it more difficult 
to bring about sufficient percussive pressure to cause explosion. 
The absorption of the nitro-glycerine in dynamite renders the lat¬ 
ter available in horizontal holes or in holes drilled upward. True 
dynamite loses only a very small percentage of its explosive power 
when saturated with water, but is then much more difficult to ex¬ 
plode. 



122 


QUARRYING. 


[CHAP. V. 


True dynamites must contain at least 50 per cent, of nitro¬ 
glycerine, otherwise the latter will he too completely cushioned 
by the absorbent, and the powder will be too difficult to explode. 
False dynamites, on the contrary, may contain as small a percentage 
of nitro-glycerine as may be desired, some containing as little as 15 
per cent. The added explosive substances in the false dynamites 
generally contain large quantities of oxygen, which are liberated 
upon explosion, and aid in effecting the complete combustion of 
any noxious gases arising from the nitro-glycerine. The false are 
generally inferior to the true dynamites, since the bulk of the 
former is increased in a higher ratio than the power; and as the 
cost of the work is largely dependent upon the size of the drill¬ 
holes, there is no economic gain. 

Dynamites which contain large percentages of nitro-glycerine 
explode with great suddenness, tending to break the rock into 
small fragments. They are most useful in blasting very hard rock. 
In such rock dynamite containing 75 per cent, of nitro-glycerine 
is roughly estimated to have about 6 times the force of an equal 
weight of gunpowder ; but in soft rock or clay its power, at equal 
cost, is inferior to that of common gunpowder, because its action 
is akin to a sudden blow, rather than to a continued push. F^r 
soft or decomposed rocks, sand, and earth, the lower grade» -A 
dynamite, or those containing a smaller percentage of nitro-glycei- 
ine, are more suitable. They explode with less suddenness, and 
their tendency is rather to upheave large masses of rock than to 
splinter small masses. 

“Judgment must be exercised as to the grade and quantity of 
explosive to be used in any given case. Where it is not objection¬ 
able to break the rock into small pieces, or where it is desired to do 
so for convenience of removal, the higher shattering grades are use¬ 
ful. Where it is desired to get the rock out in large masses, as in 
quarrying, the lower grades are preferable. For very difficult work 
in hard rock, and for submarine blasting, the highest grades, con¬ 
taining 70 to 75 per cent, of nitro-glycerine, are used. A small 
charge does the same execution as a larger charge of lower grade, 
and of course does not require the drilling of so large a hole. In 
submarine work their sharp explosion is not deadened by the 
water. For general railroad work, ordinary tunneling, mining of 
■ores, etc., the average grade, containing 40 per cent, of nitro-glycer- 




NITRO-GLYCERINE EXPLOSIVES. 


123 


ine, is used ; for quarrying, 35 per cent.; for blasting stumps, trees, 
piles, etc., 30 per cent.; for sand and earth, 15 per cent.” 

177. A great variety of dynamites is made. Each manufacturer 
usually makes a number of grades, containing different percentages 
of nitro-glycerine, and gives to his poVder some fanciful name. 
Dynamite is sold in cylindrical, paper-covered cartridges, from J of 
an inch to 2 inches in diameter, and 6 to 8 inches long, or longer, 
which are packed in boxes containing 25 or 50 pounds each. They 
are furnished, to order, of any required size. The price per pound 
ranges from 15 cents for 15 per cent, nitro-glycerine to 50 cents for 
75 per cent, nitro-glycerine. 

Table 14 (page 124) gives the names of all the explosives con¬ 
taining nitro-glycerine, with the per cent, in each case.* 

178. Ill* By Channeling and Wedging. By channeling is meant 
the process of cutting long narrow channels in rock to free the sides 
of large blocks of stone. Quite a large number of machines have 
been invented for doing this work, all of which make the channels 
by one form or the other of the machine drills already described 
(see the second paragraph of § 172). The machines are mounted 
upon a track on the bed of the quarry, and can be moved forward 
as the work progresses. If the rock is in layers, it is only necessary 
to cut the channels part way through the layer, when the block can 
be detached with wedges, the groove guiding the fracture. If the 
rock is not in layers, after the necessary channels have been cut 
around the block, it is necessary to under-cut the block in order to 
release it. This is accomplished by drilling a series of holes along 
the bottom, which process is called “ gadding” by quarry-men. The 
block is then split from its bed by means of wedges. The method 
of channeling and wedging is much employed in quarrying marble, 
the massive limestones, and the thick-bedded sandstones. The 
method is very economical and expeditious, except in granite and 
the hardest sandstones. For illustrations of the two principal chan¬ 
neling machines and also quarries being worked by this method, see 
Report on the Quarry Industry, pp. 44-52, in Vol. X. of the Tenth 
Census of the United States. 

* W. C. Foster, in Engineering News , vol. xix. p. 254. For a list of all the explo¬ 
sives employed as blasting agents, together with a description of their composition 
and references to the literature of each, see Engineering News , vol. xix. pp. 533-34, 
and vol. xx. pp. 8-10. 





124 


QUARRYING. 


/ 


[CHAP. V. 


TABLE 14. 

List of Explosives containing Nitro-glycerine. 


Name of Explosive. 

Per cent. 
t)f 

Nitro¬ 

glycerine. 

Name of Explosive. 

Per cent, 
of 

Nitro¬ 

glycerine. 

y£tna powder, No. 1. 

65 

Glyxoline. 






“ “ “ 2 XX... 

50 

Hecla powder, No. 1XX.. 

75 

t< c< <( 9 

^ • • • • • • 

40 

Gun Sawdust. 

16 to 20 

“ “ “ 3X_ 

35 

“ “ No. IX. 

50 

“ “ “ 4X... 

25 

n a a j 

40 

“ • “ “ 5. 

15 

“ “ “ 2X. 

35 

Ammonia powder. 

16 to 20 

<< it (< ^ 

30 

Asbestos powder. 

varies 

(< if a QV 

OaV, • • • « • 

25 

Atlas powder, A. 

75 

<< t< <t g 

20 

“ * “ B-f-. 

60 

Hercules powder, No. 1 XX 

75 

“ “ B. 

50 

if f f < ( -J 

65 

“ “ C+. 

45 

“ “ “ 2SSS 

55 

“ “ C. 

40 

“ “ “ 2SS.. 

50 

“ “ D-j-. 

35 

<f “ “ 2 S... 

45 

“ “ D. 

30 

f f 4 f (( g 

40 

“ “ E-f. 

25 

“ “ “ 3S... 

35 

“ “ E. 

20 

<< ft f< g 

30 

“ “ p_|_ 

15 

“ “ “ 4S... 

25 

Brady’s dynamite. 

33 

f < < f Ci A. 

a • • • • 

20 

Brain's powder. 

40 

Horsley’s powder (some 


ColOnia powder. 

40 

varieties). 

20 

Dualin (Dittmar’s). 

50 

Judson Giant Powder,No.2 

40 

Dynamite (Nobel’s, Kiesel- 


Judson powder, FFF. 

20 

gubr dynamite). 


FF. 

15 

Old No. 1 

75 

F. 

10 

Old No. 2 

40 

KRP. 

5 to 6 

Old No. 3 

25 

Lithofracteur. 

52 

Electric powder. 

33 

Metalline Nitroleum. . . . 

varies 

Explosive gelatine. 

93 

Mica powder, ISo 1 

40 

Forcite, 2 grades. 

75, 70 

if ff f< 9 

52 

Fulgurite (solid). 

60 

Miners’ Powder Co.’s Dy- 

“ (liquid). 

90 

namite. 

33 

Gelatine dynamite, A. 

97.5 

Neptune powder. 

32 7 

“ " “ No. 1.. 

58 

Nitro Toluol. 

70 

** “ “ 2 . 

38.8 

Norrbin & Oklssou’s pow- 


Gelatine explosive de 


der. 

25 to 50 

guerre. 

89.3 

PontoDolite . . . 


Gelignite. 

56.5 

Porifera Nitroleum 

• • • • 

vn ri po 

Giant powder, No. 1 . 

75 

Rendrock. 

33 4 

New “ 1 . 

50 

Sebastin, No. 1. 

78 

“ 2 extra 

45 

“ “ 2 . 

68 

f < f < i f g 

40 

Selenitic powder . 

varies 

" 2 c. 

33 

Seranim. 

“ “ “ XXX.. 

27 

Yigorite (U. S.) . 

43.8 

“ (< (t jyj 

20 

Vitrite, No. 1. 


Giant powder (Nobel’s), 


“ '' “ 2 . 


No. 2. . 

20 

Vulcan powder. 

32.6 



















































































CHAPTER VI. 


STONE CUTTING. 

Art. 1. Tools. 

179. In order to describe intelligibly the various methods of 
preparing stones for use in masonry, it will be necessary to begin 
with a description of the tools used in stone-cutting, as the names 
of many kinds of dressed stones are directly derived from those of 
the tools used in dressing them. 

With a view to securing uniformity in the nomenclature of 
building stones and of stone masonry, a committee of the American 
Society of Civil Engineers prepared a classification and recommended 
that all specifications should be made in accordance therewith. The 
old nomenclature was very unsystematic and objectionable on many 
grounds. The new system is good in itself, is recommended by the 
most eminent authority, has been quite generally adopted by en¬ 
gineers, and should therefore be strictly adhered to. The following 
description of the hand tools used in stone cutting is from the 
report of the American Society’s committee.* 

180. Hand Tools. “The Double Face Hammer, Fig. 9, is a 
heavy tool weighing from 20 
to 30 pounds, used for rough¬ 
ly shaping stones as they 
come from the quarry and 
for knocking off projections. 

This is used only for the Fig. 9.—double Face hammer. 

roughest w T ork. 

“ The Face Hammer, Fig. 10, has one blunt and one cutting 
end, and is used for the same 
purpose as the double face 
hammer where less weight is C 
required. The cutting end 
is used for roughly squaring 

stones, preparatory to the use fig. io.—Face Hammer. 

of finer tools. 







0 



V 


« 3 “ > 


J 


* Trans. Am. Soc. of C. E., vol. vi. pp. 297-304. 


125 






















126 


STONE CUTTING. 


[CHAP. VT. 




“The Cavil, Fig. 11, has one blunt and one pyramidal, or 
pointed, end, and weighs from 15 to 20 pounds. 
It is used in quarries for roughly shaping stone 
for transportation. 

The Pick, Fig. 12, somewhat resembles the 
Fig. ii.—Cavil, pick used in digging, and is used for rough dress¬ 
ing, mostly on limestone and sandstone. Its length varies from 
15 to 24 inches, the thickness 
at the eye being about 2 
inches. 

“ The Ax, or Pean Ham¬ 
mer, Fig. 13, has two opposite 
cutting edges. It is used for 
making drafts around the arris, 
or edge, of stones, and in re¬ 
ducing faces, and sometimes FlG - 12 - —PlcK - 

joints, to a level. Its length is about 10 inches, and the cutting 

edge about 4 inches. It is used after 
the point and before the patent ham¬ 
mer. 

“The Tooth Ax, Fig. 14, is like 
fig. 13.—a.x. the ax, except that its cutting edges 

are divided into teeth, the number of which varies with the kind 
of work required. This tool 
is not used in granite and 
gneiss cutting. 

“ The Bush Ham rn e r, 

Fig. 15, is a square prism of 
steel whose ends are cut into 
a number of pyramidal points. Fig - 14 -—'Tooth ax. 

The length of the hammer is from 4 to 8 inches, and the cutting 

face from 2 to 4 inches square. 
The points vary in number and 
in size with the work to be done. 
One end is sometimes made 
with a cutting edge like that of 
the ax. 


( 


< v 



* 3 • » 


c 


3 - 


0 


66 


Fig. 15.—Bush Hammer. 

The Crandall, Fig. 16, is a malleable-iron bar about two feet 






























ART. 1.] 


TOOLS. 


127 


c 


O* C 


. zv , 


Fig. 16.—Crandall. 


0 




- > 


J 


t Z 

.. 

Fig. 17.- 


long, slightly flattened at one end. In this end is a slot 3 inches 
long and § inch wide. Through this 
slot are passed ten double-headed 
points of ^-inch square steel, 9 
inches long, which are held in 
place by a key. 

“The Patent Hammer, Fig. 

17, is a double-headed tool so 
formed as to hold at each end a set of wide thin chisels. The tool 

is in two parts, which are held to¬ 
gether by the bolts which hold the 
chisels. Lateral motion is prevented 
by four guards on one of the pieces. 
Patent Hammer. The tool without the teeth is 

5-Jx2|X H inches. The teeth are 2f inches wide. Their thickness 
varies from ^ 1° f °f an inch. This tool is 
used for giving a finish to the surface of stones. 

“ The Hand Hammer, Fig. 18, weighing 
from 2 to 5 pounds, is used in drilling holes, fig. is.—hand Hammer. 
and in pointing and chiseling the harder rocks. 

“ The Mallet, Fig. 19, is used where the softer limestones and 

sandstones are to be cut. 

“The Pitching Chisel, Fig. 20, 
is usually of 1^-inch octagonal steel, 
spread on the cutting edge to a 
rectangle of X 2£ inches. It is 
used to make a well-defined edge to 
the face of a stone, a line being marked on the joint surface to 
which the chisel is applied and the portion of the stone outside of 
the line broken off by a blow with the hand-hammer on the head 
of the chisel. 

“The Point, Fig. 21, is made of round or octagonal rods of 
steel, from \ inch to 1 inch in diameter. It is made about 12 
inches long, with one end brought to a point. 






Fig. 21.—Point. 




It is used until its length is reduced to about d 
5 inches. It is employed for dressing off the (£ 
irregular surface of stones, either for a perma¬ 
nent finish or preparatory to the use of the ax. 

According to the hardness of the stone, either the hand-hammer 
or the mallet is used with it. 



















































128 


STONE CUTTING. 


[CHAP. VI. 


“ The Chisel, Fig. 22, of round steel of J to f inch in diameter 

and about 10 inches long, with one end brought 
to a cutting edge from J inch to 2 inches 
wide, is used for cutting drafts or margins on 
the face of stones. 



fig. 22 .— Chisel. “ The Tooth Chisel, Fig. 23, is the same 

as the chisel, except that the cutting edge is divided into teeth. 
It is used only on mar- 

“ d 


Cc 


Fig. 23. 

Tooth Chisel. 




Fig. 24. 

Splitting Chisel. 


bles and sandstones. 

“ The Splitting Q 
Chisel, Fig. 24, is used 
■chiefly on the softer, 
stratified stones, and sometimes on fine architectural carvings in 
granite. 

<e The Plug, a truncated wedge of steel, and the Feathers of 
lialf-round malleable iron, Fig. 25, are used for splitting unstrati¬ 
fied stone. A row of holes is made with the Drill, Fig. 26, on the 



Fig. 25. Fig. 26.— Drills. 

Plug and Feathers. 


line on which the fracture is to be made ; in each of these holes 
two feathers are inserted, and the plugs lightly driven in between 
them. The plugs are then gradually driven home by light blows 
of the hand hammer on each in succession until the stone splits.” 

181. Machine Tools. In all large stone-vards machines are 
used to prepare the stone. There is great variety in their form, 
but since the surface never takes its name from the tool which 
forms it, it will be neither necessary nor profitable to attempt a de¬ 
scription of individual machines. They include stone-saws, stone¬ 
cutters, stone-planers, stone-grinders, and stone-polishers. 

The saws may be either drag, circular, or band saws ; the cut¬ 
ting may be done by sand and water fed into the kerf, or by carbons 
or black diamonds. Several saws are often mounted side by side and 
operated by the same power. 

The term “ stone-cutter” is usually applied to the machine which 
















































ART. 2.] 


METHOD OF FORMING SURFACES. 


129 


attacks the rough stone and reduces the inequalities somewhat. 
After this treatment the stone goes in succession to the stone- 
planer, stone-grinder, and stone-polisher. 

Those stones which are homogeneous, strong and tough, and 
comparatively free from grit or hard spots, can be worked by ma¬ 
chines which resemble those used for iron ; but the harder, more 
brittle stones require a mode of attack more nearly resembling that 
employed in dressing stone by hand. Stone-cutters and stone- 
planers employing both forms of attack are made. 

Stone-grinders and stone-polishers differ only in the degree of 
fineness of the surface produced. They are sometimes called “rub¬ 
bing-machines.” Essentially they consist of a large iron plate re¬ 
volving in a horizontal plane, the stone being laid upon it and braced 
to prevent its sliding. The abradent is sand, which is abundantly 
supplied to the surface of the revolving disk. A small stream of 
water works the sand under the stone and also carries away the 
debris. 


Art. 2. Method of forming the Surfaces. 

182. It is important that the engineer should understand the 
methods employed by the stone-cutter in bringing stones to any re¬ 
quired form. The surfaces most frequently required in stone cutting 
are plane, cylindrical, warped, Eelicoidal, conical, spherical, and 
sometimes irregular surfaces. 

183. Plane Surfaces. In squaring up a rough stone, the first 
thing the stone-cutter does is to draw a line, with iron ore or black 
lead, on the edges of the stone, to indicate as nearly as possible the 
required plane surface. Then with the hammer and the pitching- 
tool he pitches off all debris or waste material above the lines, 
thereby reducing the surface approximately to a plane. With a 
chisel he then cuts a draft around the 
edges of this surface, ?. e., he forms nar¬ 
row plane surfaces along the edges of the 
stone. To tell when the drafts are in 
the same plane, he uses two straight¬ 
edges having parallel sides and equal 
widths. See Fig. 27. The projections 
on the surface are then removed by the pitching chisel or the point, 
until the straight-edge will just touch the drafts and the inter¬ 
mediate surface when applied across the stone in any direction. 












130 


STONE CUTTING. 


[CHAP. VI. 


The surface is usually left a little “ slack,” i. e., concave, allow 
room for the mortar ; however, the surface should be but a very 
little concave. 

The surface is then finished with the ax, patent hammer, buaa 
hammer, etc., according to the degree of smoothness required. 

184. To form a second plane surface at right angles to the first 
one, the workman draws a line on the cut face to form the inter¬ 
section of the two planes ; he also draws a line on the ends of the 
stone approximately in the required plane. With the ax or the 
chisel he then cuts a draft at each end of the stone until a steel 
square fits the angle. He then joins these drafts by two others at 
right angles to them, and brings the whole surface to the same 
plane. The other faces may be formed in the same way. 

If the surfaces are not at right angles to each other, a bevel is 
used instead of a square, the same general method being pursued. 

185. Cylindrical Surfaces. These may be either concave or 
convex. The former are frequently required, as in arches; and the 
latter sometimes, as in the outer end of the face-stones of an arch. 
The stone is first reduced to a paralellopipedon, after which the 
curved surface is produced in either of two ways : (1) by cutting 
a circular draft on the two ends and applying a straight-edge along 
the rectilinear elements (Fig. 28); or (2) by cutting a draft along 
the line of intersection of the plane and cylindrical surface, and 
applying a curved templet to the required surface (Fig. 29). 



Fig. 28. 


Fig. 29. 


186. Conical Surfaces may be formed by a process very similai 
to the first one given above for cylindrical surfaces. Such surfaces 
are seldom used. 

187. Spherical Surfaces are sometimes employed, as in domes. 
They are formed by essentially the same general method as cylin¬ 
drical surfaces. 

188. Warped Surfaces. Under this head are included what 












ART. 3.J 


METHODS OF FINISHING SURFACES. 


131 


the stone-cutters call “ twisted surfaces, ” helicoidal surfaces, and 
the general warped surface. None of 
these are common in ordinary stone-work. 

The method of forming a surface 
equally twisted right and left will be de¬ 
scribed ; by obvious modifications the same 
method can be applied to secure other 
forms. Two twist rules are required, the 
angle between the upper and lower edges 
being half of the required twist. Drafts are then cut in the ends of 
the stone until the tops of the twist rules, when applied as in Fig. 
30, are in & plane. The remainder of the projecting face is removed 
until a straight-edge, when applied parallel to the edge of the stone,, 
will just touch the end drafts and the intermediate surface. 

If the surface is to be twisted at only one end, a parallel rule 
and a twist rule are used. 

189. Making the Drawings. The method of making work¬ 
ing drawings for constructions in stone will appear in subsequent 
chapters, in connection with the study of the structures them¬ 
selves; but for detailed instructions, see the text-books on Stere- 
otomy or Stone Cutting. 

Art. 3. Methods of Finishing the Surfaces.* 

190. “All stones used in building are divided into three classes, 
according to the finish of the surface; viz. : 

I. Rough stones that are used as they come from the quarry. 

II. Stones roughly squared and dressed. 

III. Stones accurately squared and finely dressed. 

“ In practice, the line of separation between them is not very 
distinctly marked, but one class gradually merges into the next. 

191. I. “Unsquared Stones. This class covers all stones 
which are used as they come from the quarry, without other 
preparation than the removal of very acute angles and excessive pro¬ 
jections from the general figure. The term backing/.which is 
frequently applied to this class of stone, is inappropriate, as it prop¬ 
erly designates material used in a certain relative position in a wall, 
whereas stones of this kind may be used in any position. 

192. II. “ Squared Stones. This class covers all stones that 

* This article is taken from the report of the committee of the American Society 
of Civil Engineers previously referred to. 















13a 


STONE CUTTING. 


[CHAP. VI. 


are roughly squared and roughly dressed on beds and joints. The 
dressing is usually done with the face hammer or ax, or in soft 
stones with the tooth hammer. In gneiss it may sometimes be 
necessary to use the point. The distinction between this class and 
the third lies in the degree of closeness of the joints. Where the 
dressing on the joints is such that the distance between the general 
planes of the surfaces of adjoining stones is one half inch or more, 
the stones properly belong to this class. 

“ Three subdivisions of this class may be made, depending on 
the character of the face of the stones: 

“ (a) Quarry-faced stones are those whose faces are left un¬ 
touched as they come from the quarry. 

f<r (b) Pitch-faced stones are those on which the arris is clearly 
defined by a line beyond which the rock is cut away by the pitching 
chisel, so as to give edges that are approximately true. 

“ ( c ) Drafted Stones are those on which the face is surrounded by 
a chisel draft, the space inside the draft being left rough. Ordi¬ 
narily, however, this is done only on stones in which the cutting of 
the joints is such as to exclude them from this class. 

“ In ordering stones of this class the specifications should always 
state the width of the bed and end joints which are expected, and 
also how far the surface of the face may project beyond the plane 
of the edge. In practice, the projection varies between 1 inch and 
6 inches. It should also be specified whether or not the faces are to 
be drafted. 

193. Ill “ Cut STONES. This class covers all squared stones 
with smoothly-dressed beds and joints. As a rule, all the edges of 
cut stones are drafted, and between the drafts the stone is smoothly 
dressed. The face, however, is often left rough where construction 
is massive. 

‘ ‘ In architecture there are a great many ways in which the faces 


of cut stone may be dressed, 
but the following are those 
that will usually be met in 
engineering work: 



“ Bough-pointed. When it 

is necessary to remove an inch 
or more from the face of a 


Fig. 31.— Rough-pointed. 


stone, it is done by the pick or heavy point until the projections 










METHODS OF FINISHING SURFACES. 


133 


ART. 3.] 


~SA 






. - I I *. w 

K ^ ^ ( _ ^ 

y o' ^ ^ •* 

nS v s-'> ^ ^ ^ -C1-. s" x '-X 

v^- Vo -5o^>C c 

\\S S ' -si S . s ^ N vs. ^ v, ^ 

V -\* '' v ' < 5 t V-'X r i X’ C ? 



Fig. 32.—Fine-pointed. 


vary from £ inch to 1 inch. The stone is then said to be rough- 
pointed (Fig. 31). In dressing 
limestone and granite, this 
operation precedes all others. 

“ Fine-pointed. (Fig. 32). 

If a smoother finish is desired, 
rough pointing is followed by 
fine pointing, which is done 
with a fine point. Fine point¬ 
ing is used only where the finish made by it is to be final, and never 
as a preparation for a final finish by another tool. 

“ Crandalied. This is only a speedy method of pointing, the 
effect being the same as fine pointing, except that the dots on the 
stone are more regular. The variations of level are about £ inch, 
and the rows are made parallel. When other rows at right angles 
to the first are introduced, the stone is said to be cross-crandalied. 
Tig. 33. 



Fig. 33.— Crandalled. 


Fig. 34.—Axed. 


“ Axed, or Pean-hammered, and Patent-hammered. These two 
vary only in the degree of smoothness of the surface which is pro¬ 
duced. The number of blades in a patent hammer varies from 6 to 
12 to the inch; and in precise specifications the number of cuts to 
the inch must be stated, such as 6-cut, 8-cut, 10-cut, 12-cut. The 
effect of axing is to cover the surface with chisel marks, which are 
made parallel as far as practicable. Fig. 34. Axing is a final finish. 

“ Tooth-axed. The tooth-ax is practically a number of points, 
and it leaves the surface of a stone in the same condition as fine 
pointing. It is usually, however, only a preparation for bush-ham¬ 
mering, and the work is then done without regard to effect so long 
as the surface of the stone is sufficiently leveled. 

“ Bush-hammered. The roughnesses of a stone are pounded off by 












































134 


STOKE CUTT1HG. 


[CHAP. VI., 


the bush hammer, and the stone is then said to be ‘bushed/ 



Fig. 35.— Bush-hammered. 


This kind of finish is dangerous 
on sandstone, as experience has 
shown that sandstone thus treated 
is very apt to scale. In dressing 
limestone which is to have a hush- 
hammered finish, the usual se¬ 
quence of operation is (1) rough¬ 
pointing, (2) tooth-axing, and (3) 


bush-hammering. Fig. 35. 

“ Rubbed. In dressing sandstone and marble, it is very common 

to give the stone a plane surface at once --- 

by the use of the stone-saw [§ 181]. Any 
roughnesses left by the saw are removed 
by rubbing with grit or sandstone [§ 181]. 

Such stones, therefore, have no margins. 

They are frequently used in architecture L__ 

for string-courses, lintels, door-jambs, etc.; Fig. 36,-rubbed. 


and they are also well adapted for use in facing the walls of lock- 
chambers and in other localities where a stone surface is liable to be 
rubbed by vessels or other moving bodies. Fig. 36. 

“ Diamond Panels. Sometimes the space between the margins 

is sunk immediately adjoining them and 
then rises gradually until the four planes 
form an apex at the middle of the panel. 
In general, such panels are called diamond 
panels, and the one just described. Fig. 
37, is called a sunk diamond panel. 
When the surface of the stone rises grad¬ 
ually from the inner lines of the margins 
to the middle of the panel, it is called a 
raised diamond panel. Both kinds of finish are common on bridge 
quoins and similar work. The details of this method should be 
given in the specifications.” 



Fig. 37.—Diamond Panel. 


















CHAPTER VII. 


STONE MASONRY. 

In preparing specifications, it is not safe to depend alone upon 
the terms in common use to designate the various classes of masonry; 
but every specification should contain an accurate description of the 
character and quality of the work desired. Whenever practicable, 
samples of each kind of cutting and masonry should be prepared 
beforehand, and be exhibited to the persons who propose to under¬ 
take the work. 

194. Definitions of Parts of the Wall.* Face, the front 
surface of a wall; bach, the inside surface. 

Facing, the stone which forms the face or outside of the wall. 
Backing, the stone which forms the back of the wall. Filling, the 
interior of the wall. 

Batter. The slope of the surface of the wall. 

Course. A horizontal layer of stone in the wall. 

Joints. The mortar-layer between the stones. The horizontal 
joints are called bed-joints or simply beds', the vertical joints are 
sometimes called the builds. Usually the horizontal joints are 
called beds , and the vertical ones joints. 

Coping. A course of stone on the top of the wall to protect it. 

Pointing. A better quality of mortar put in the face of the 
joints to help them to resist weathering. 

Bond. The arrangement of stones in adjacent courses (§ 202). 

Stretcher. A stone whose greatest dimension lies parallel to the 
face of the wall. 

Header. A stone whose greatest dimension lies perpendicular 
to the face of the wall. 

Quoin. A corner-stone. A quoin is a header for one face and a 
stretcher for the other. 

Doicels . Straight bars of iron which enter a hole in the upper 
side of one stone and also a hole in the lower side of the stone next 
above. 

Cramps. Bars of iron having the ends turned at right angles to 

* The definitions in this chapter are in accordance with the recommendations of 
the Committee of the American Society of Civil Engineers previously referred to, 
and conform to the best practice. Unfortunately they are not universally adopted. 

135 - 



136 


STONE MASONRY. 


[CHAP. YIH 


to the body of the bar, which enter holes in the npper side of ad¬ 
jacent stones. 


195. Definitions of Kinds of Masonry. Stone masonry is 
classified (1) according to the degree of finish of the face of the 
stones, as quarry-faced, pitch-faced, pointed, hush-hammered, etc.; 
(2) according to whether the horizontal joints are more or less con¬ 
tinuous, as range, broken range, and random; and (3) according 
to the care employed in dressing the beds and joints, as ashlar, 
squared-stone, and rubble. 



Fig. 38. 


Fig. 39. 


196. Quarry-facecl Masonry. That in 
which the face of the stone is left as it 
comes from the quarry. Fig. 38. 

Pitch-faced Masonry. That in which 
the face of the stone is roughly dressed 
(§ 192, h). Fig. 39. The front of a 
horizontal joint is a straight line. 

The preceding are the most common in engineering masonry; 
for additional methods of finishing the face, see §§ 190-193. 

197. Range. Masonry in which a course is of the same thick¬ 
ness throughout. Fig. 40. 

Broken Range. Masonry in which a course is not continuous 
throughout. Fig. 41. 

Random. Masonry which is not laid in courses at all. Fig. 42. 



rr~T~ i- 








— 1 H ' 

1— 

h 

r-L) 




v 






— 







—r 


















nz 




Fig. 41.— Broken Range. Fig. 49.— Random. 


Any one of these three terms may be employed to designate the 
coursing of either ashlar (§196) or square-stone masonry (§ 197), 
but can not be applied to rubble (§ 198). 

198. Ashlar. Cut-stone masonry, or masonry composed of any 
of the various kinds of cut-stone mentioned in § 193. According 
to the Report of the Committee of the American Society of Civil 
Engineers, “ when the dressing of the joints is such that the dis¬ 
tance between the general planes of the surfaces of adjoining stones 
is one half inch or less, the masonry belongs to this class.” From 






















































































































































DEFINITIONS OF KINDS OF MASONRY. 


137 


its derivation ashlar apparently means large, square blocks; but 
practice seems to have made it synonymous with “ cut-stone,” and 
this secondary meaning lias been retained for convenience. The 
coursing of ashlar is described by prefixing range, broken range, 
or random; and the finish of the face is described by prefixing the 
name of the cut-stone (see'^§‘190—93) of which the masonry is 
composed. 

Small Ashlar. Cut-stone masonry in which the stones are less 
than one foot thick. The term is not often used. 

Rough Ashlar. A term sometimes given to squared-stone 
masonry (§197), either quarry-faced or pitch-faced, when laid as 
range-work; but it is more logical and more expressive to call such 
work range squared-stone masonry. 

Dimension Stones. Cut-stones, all of whose dimensions have 
been fixed in advance. “ If the specifications for ashlar masonry 
are so written as to prescribe the dimensions to be used, it will not 
be necessary to make a new class for masonry composed of such 
stones.” 

Squared-stone Masonry. Work in which the stones are roughly 
squared and roughly dressed on beds and joints (§M9.2). The 
distinction between squared-stone masonry and ashlar (§-196) 
lies in the degree of closeness of the joints. According to the 
Report of the Committee of the American Society of Civil Engineers, 
“ when the dressing on the joints is such that the distance between 
the general planes of the surface of adjoining stones is one half inch 
or more, the stones properly belong to this class;” nevertheless, 
such masonry is often classed as ashlar or cut-stone masonry. 

Rubble Masonry. Masonry composed of unsquared stone 


(§ 191). 

Uncoursed Rubble. Masonry composed of unsquared stones 
laid without any at¬ 
tempt at regular 
courses. Fig. 43. 

Coursed Rubble. 

Unsquared-stone ma¬ 
sonry which is leveled 
off at specified heights 

1 , Fig. 43. Fig. 44. 

to an approximately 

horizontal surface. It may be specified that the stone shall be rough¬ 
ly shaped with the hammer, so as to fit approximately. Fig. 44. 






































































































138 


STONE MASONRY. 


[CHAP. YII. 


199. General Rules. Rankine gives the following rules to "be 
observed in the building of all classes of stone masonry: 

“ I. Build the masonry, as far as possible, in a series of courses, 
perpendicular, or as nearly so as possible, to the direction of the 
pressure which they have to bear; and by breaking joints avoid all 
long continuous joints parallel to that pressure. 

“ II. Use the largest stones for the foundation course. 

“ III. Lay all stones which consist of layers in such a manner that 
the principal pressure which they have to bear shall act in a direction 
perpendicular, or as nearly so as possible, to the direction of the 
layers. This is called laying the stone on its natural heel, and is of 
primary importance for strength and durability. 

“IV. Moisten the surface of dry and porous stones before bed¬ 
ding them, in order that the mortar may not be dried too fast and 
reduced to powder by the stone absorbing its moisture. 

“ V. Fill every part of every joint, and all spaces between the 
stones, with mortar, taking care at the same time that such spaces 
shall be as small as possible.” 

Another and very important rule is: the rougher the stones, the 
better the mortar should be. The principal object of the mortar is 
to equalize the pressure; and the more nearly the stones are reduced 
to closely fitting surfaces, the less important is the mortar. Not 
infrequently this rule is exactly reversed; i. e., the finer the dressing, 
the better the quality of the mortar used. 

200. Ashlar Masonry. For definitions of this class of masonry 
and its subdivision, see § 196. 

The strength of a mass of ashlar masonry depends upon the 
size of the blocks in each course, upon the accuracy of the dressing, 
and upon the bond. 

In order that the stones mav not be liable to be broken across, 
no soft stone, such as the weaker kinds of sandstone and granular 
limestone, should have a length greater than 3 times its depth; but 
in harder materials, the length may be 4 or 5 times the depth. The 
breadth in soft materials may range from 1^ to 2 times the depth ; 
in hard materials, it may be 3 times the depth. 

201. Dressing. The closeness with which stones fit is depend¬ 
ent solely upon the accuracy with which the surfaces in contact are 
wrought, or dressed, and is of special importance in the case of 
bed-joints. If any part of the surface projects beyond the plane 



ASHLAR MASOHRY. 


139 


of the chisel-draft, that projecting part will have to hear an undue 
share of the pressure, the joint will gape at the edges,—constituting 
what is called an open joint ,—and the whole will he wanting in 
stability. On the other hand, if the surface of the bed is concave, 
havihg been dressed down below the plane of the chisel-draft, the 
pressure is concentrated on the edges of the stone, to the risk of 
splitting them off. Such joints are said to be flushed. They are 
more difficult of detection, after the masonry has been built, than 
open joints ; and are often executed by design, in order to give a 
neat appearance to the face of the building. Their occurrence 
must therefore be guarded against by careful inspection during 
the progress of the stone cutting. 

G reat smoothness is not desirable in the joints of ashlar masonry 
intended for strength and stability ; for a moderate degree of rough¬ 
ness adds at once to the resistance to displacement by sliding, and 
to the adhesion of the mortar. When the stone has been dressed 
so that all the small ridges and projecting points on its surface are 
reduced nearly to a plane, the pressure is distributed nearly uni¬ 
formly, for the mortar serves to transmit the pressure to the small 
depressions. Each stone should first be fitted into its place dry, 
in order that any inaccuracy of figure may be discovered and cor¬ 
rected by the stone-cutter before it is finally laid in mortar and 
settled in its bed. 

The thickness of mortar in the joints of the very best ashlar 
masonry—for example, the United States post-office and custom¬ 
house buildings in the principal cities—is about -J of an inch ; in 
first-class railroad masonry—for example, important bridge piers 
and abutments, and large arches—the joints are from to % 
of an inch. No cutting should be allowed after the stone 
has been set in mortar, for fear of breaking the adhesion of the 
mortar. 

A chisel-draft or 2 inches wide is usually cut at each exterior 
corner. 

202. Bond. No side-joint of any course should be directly above 
a side-joint in the course below ; but the stones should overlap, or 
break joint , to an extent of from 1 to 1J times the depth of the 
course. This is called the bond of the masonry. The effect is that 
each stone is supported by at least two stones of the course below, and 
assists in supporting at least two stones of the course above. The 



140 


STCWE MASOISTRY. 


[CHAP. VII. 


object is twofold : first, to distribute the pressure, so that inequali¬ 
ties of loud on the upper part of the structure (or of resistance at 
the foundation) may be transmitted to and spread over an increas¬ 
ing area' of bed in proceeding downwards (or upwards); and second, 
to tie the building together, i. e., to give it a sort of tenacity, both 
lengthwise and from face to back, by means of the friction of the 
stones where they overlap. 

The strongest bond is that in which each course at the face of 
the structure contains a header and a stretcher alternately, the 
outer end of each header resting on the middle of a stretcher of 
the course below, so that rather more than one third of the area of 
the face consists of ends of headers. This proportion may be 
deviated from when circumstances require it, but in every case it 
is advisable that the ends of headers should not form less than one 
fourth of the whole area of the face of the structure. A header 
should extend entirely through the wall, and should be over the 
middle of the stretcher in the course below. 

A trick of masons is to use “ blind-headers ,” or short stones that 
look like headers on the outside but do not go deeper into the wall 
than the adjacent stretchers. When a course has been put on top 
of these, they are completely covered up ; and, if not suspected, 
the fraud will never be discovered unless the weakness of the w r all 
reveals it. 

Where very great resistance to displacement of the masonry is 
required (as in the upper courses of bridge piers, or over openings, 
or where new masonry is joined to old, or where there is danger of 
unequal settlement), the bond is strengthened by dowels or by 
cramp-irons (§ 195) of, say, lj-inch round iron set with cement 
mortar. 

203. Backing. Ashlar is usually backed with rubble masonry 
(§ 213), which in such cases is specified as coursed rubble. Special 
care should be taken to secure a good bond between the rubble 
backing and the ashlar facing. Two stretchers of the ashlar fac¬ 
ing having the same width should not be placed one immediately 
above the other. The proportion and length of the headers in 
the rubble backing should be the same as in the ashlar facing. The 
“ tails of the headers, or the parts which extend into the rubble 
backing, may be left rough at the back and sides; but their upper 
and lower beds should be dressed to the general plane of the bed of 



ASHLAR MASOHRY. 


141 


the course. These “ tails” may taper slightly in breadth, but should 
not taper in depth. 

The backing should be carried up at the same time with the 
face-work, and in courses of the same depth; and the bed of each 
course should be carefully built to the same plane with that of the 
ashlar facing. The rear face of the backing should be lined to a 
fair surface. 

204. Pointing. In laying masonry of any character, whether 
with common or hydraulic mortar, the exposed edges of the joints 
will naturally be deficient in density and hardness. The mortar in 
the joints near the surface is especially subject to dislodgment, 
since the contraction and expansion of the masonry is liable either 
to separate the stone from the masonry or to crack the mortar in 
the joint, thus permitting the entrance of rain-water, which, freezing, 
forces the mortar from the joints. Therefore it is usual, after the 
masonry is laid, to refill the joints as compactly as possible, to the 
depth of at least half an inch, with mortar prepared especially for 
this purpose. This operation is called pointing. 

The very best cement mortar should be used for pointing, as the 
best becomes dislodged all too soon. Clear Portland cement mor¬ 
tar is the best, although 1 volume of cement to 1 of sand is fre¬ 
quently used in first-class work. The mortar, when ready for use, 
should be rather incoherent and quite deficient in plasticity. Before 
applying the pointing, the joint should be well cleansed by scrap¬ 
ing and brushing out the loose matter, and then be well moistened. 
Of course, the cleansing out of the joints can be most easily done 
while the mortar is new and soft. The depth to which the mortar 
shall be dug out is not often specified ; it is usually cleaned out 
about half .an inch deep, but should be at least an inch. In the 
Brooklyn bridge piers the joints were cleared 1J inches deep. 

The mortar is applied with a mason’s trowel, and the joint well 
calked with a calking iron and hammer. In the very best work, 
the joint is also rubbed smooth with a steel polishing tool. Walls 
should not be allowed to dry too rapidly after pointing; therefore, 
pointing m hot weather should be avoided. 

205. Amount of Mortar. The amount of mortar required for 
ashlar masonry varies with the size of the blocks, and also with 
the closeness of the dressing. With §- to -J-inch joints and 12- to 
20-inch courses, there will be about 2 cubic feet of mortar per 



142 


STONE MASONRY. 


[CHAP. VII* 


cubic yard; with larger blocks and closer joints, i. e ., in the best 
masonry, there will be about 1 cubic foot of mortar per yard of 
masonry. Laid in 1 to 2 mortar, ordinary ashlar will require £ to 
£ of a barrel of cement per cubic yard of masonry. 

For the quantities of cement and sand required for a cubic yard 
of mortar of different compositions, see page 88. 

206. When Employed. Ashlar masonry is used for piers, abut¬ 
ments, arches, and parapets of bridges; for hydraulic works; for 
facing-quoins, and string courses; for the coping of inferior kinds 
of masonry and of brick w T ork; and, in general, for works in which 
great strength and stability are required. 

207. Specifications for Ashlar. The specifications for ashlar, 
or “ first-class masonry ” as employed on the railroads, are about 
as follows: * * * § 

Ashlar shall consist of range pitch-faced masonry. The stone shall be of 
durable quality; and shall be free from seams, powder cracks, drys, flaws, or 
other imperfections. • 

All foundation courses shall be laid with selected, large, flat stones not less 

than -f inches in thickness, nor of less superficial surface than fifteen (15) 

square feet. 

The courses shall be not less than-inches thick nor more than- 

inches.:}: The courses shall be continuous around and through the wall; and 
no course shall be thicker than the one below it, except that the footing 
course may be thinner than the one next above. Stretchers shall be at least 
twice as wide as thick, and at least four times as long as thick. Headers shall 
be, for at least three fourths of their length, not less than twice as wide as 
thick; and shall extend entirely through the wall, or have a length not less 
than five times the thickness of the course. The masonry shall consist of 
headers and stretchers alternating; at least one third § of the face of the wall 
shall consist of headers. Stretchers of the same width shall not be placed 
immediately one above the other ; but this shall not apply to the ends of 
stretchers where headers come centrally between stretchers. Ever}-- header 
shall be immediately over a stretcher of the course next below. Joints on the 
face of the wall shall be broken at least three quarters of the thickness of the 
course. 

The beds and the vertical joints for 12 inches back from the face of the 
wall shall be dressed, before being brought to the wall, so as to form mortar 

* For complete specifications for railroad and also other kinds of masonry, see 
Appendix I, page 529. 

f Frequently 12; sometimes 18. 

X The courses of the classes of masonry referred to above usually range from 
14 to 30 inches; but, of course, may vary according to the circumstances, and for 
some purposes may be as low as 10 inches. 

§ Often specified as one fourth. 








I 


SQUARE-STONED MASONRY. 143'. 


joints not less than one quarter inch nor more than one half inch in thickness. 
All stones shall be laid on the natural bed. No part of a stone shall extend 
beyond the back edge of the under bed. All corners and hatter lines shall 
have a neat chisel-draft one and one half inches wide on each face. The pro¬ 
jections of the rock-face must not exceed four inches beyond the draft-lines ; 
and in tunnel side-walls, the projection must not exceed two inches. The. 
face-edge of the joint shall be pitched to a straight line. 

The backing shall consist of stone of the same thickness as the correspond¬ 
ing face stone. When walls exceed four feet in thickness, there shall be as 
many headers of the same size in the back of the wall as in the face, so ar¬ 
ranged that a header in the rear of the wall shall be between two headers in 
the front. The backing shall be so laid as to leave no spaces between the 
stones over six inches wide, which spaces shall be filled with spalls set in 
cement mortar. No spalls shall be allowed in the bed joints. 

The coping shall be formed of large flat stones, which shall extend entirely 
across the wall when the same is not more thau six feet wide. The steps of 
wing walls shall be capped with stone covering the entire step and extending 
under the step next above at least twelve inches. Coping and step stones shall 
be at least twelve inches thick, and have such projections as the engineer may 
direct [usually 3 to 6 inches]. The tops and faces of copings and step stones 
shall be bush-hammered, and their joints and beds cut to one quarter inch 
throughout. 

208. Squared-stone Masonry. For definitions of this class of 
masonry and its subdivisions, see g 197. The distinction between 
squared-stone masonry and ashlar lies in the degree of closeness of 
the joints. According to the Report of the Committee of the 
American Society of Civil Engineers, “ when the dressing on the 
joints is such that the distance between the general planes of the 
surfaces of adjoining stones is one half inch or more, the stones 
properly belong to this class;” however, such masonry is usually 
classed as ashlar or cut-stone masonry. 

Squared-stone masonry is usually quarry-faced, random-work, 
although pitch-faced range-work is not uncommon. The quoins 
and the sides of openings are usually reduced to a rough-smooth 
surface with the face-hammer, the ordinary ax, or the tooth-ax. 
This work is a necessity where door or window frames are inserted; 
and it greatly improves the general effect of the wall, if used 
wherever a corner is turned. 

209. Squared-stone masonry is distinguished, on the one hand, 
from ashlar in having less accurately dressed beds and joints, and, on 
the other hand, from rubble in being more carefully constructed. 
In ordinary practice, the field covered by this class is not very 
definite. The specifications for “ second-class masonry” as used 




144 


STOKE MASOKRY. 


[OHAP. YTI. 


on railroads usually conform to the above description of quarry-faced, 
range squared-stone masonry; but sometimes this grade of masonry 
is designated “ superior rubble.” 

210. Amount of Mortar Required. The amount of mortar 
required for squared-stone masonry varies with the size of the 
stones and with the quality of the masonry; as a rough average, 
one sixth to one quarter of the mass is mortar. When laid in 1 to 
2 mortar, squared-stone masonry will require to f of a barrel of 
cement per cubic yard of masonry. 

For quantities of cement and sand required for mortars of 
various compositions, see the table on page 88. 

211. Backing and Pointing. The statements concerning the 
backing and pointing of ashlar (§§ 203 and 204) apply substantially 
to squared-stone masonry. As the joints of squared-stone masonry 
are thicker than those of ashlar, the pointing should be done pro¬ 
portionally more carefully; while as a rule it is done much more 
carelessly. The mortar is often thrown into the joint with a 
trowel, and then trimmed top and bottom to give the appearance 
of a thinner joint. Such work is called ribbon pointing. Trimming 
the pointing adds to the appearance but not to the durability. 
When not trimmed it is called dashed pointing. 

212. Specifications for Squared-stone Masonry. Squared-stone 
masonry is employed for the piers and abutments of lighter bridges, 
for small arches, for box-culverts, for basement walls, etc. The 
specifications are about as follows: * 

The stones shall be of durable quality; and shall be free from seams, 
powder cracks, drys, or other imperfections. 

The courses shall be not less than 10 inches thick. 

Stretchers shall be at least twice as wide as thick, and at least four times as 
long as thick. Headers shall be at least five times as long as thick, and at least 
as wide as thick. There shall be at least one header to three stretchers. Joints 
on the face shall be broken at least 8 inches. 

The beds and vertical joints for 8 inches back from the face of the wall 
shall be dressed to make joints one half to one inch thick. The front edge of 
the joint shall be pitched to a straight line. All corners and batter-lines shall 
be hammer-dressed. 

The backing shall consist of stones not less in thickness than the facing. 
At least one half of the backing shall be stones containing 2 cubic feet. 
The backing shall be laid in full mortar beds; and the vertical joints shall 


* For complete specifications for masonry for various purposes, see Appendix I 
page 529. 







RUBBLE MASONRY. 


145 


also be tilled with mortar. The spaces between the large stones shall be filled 
with spalls set in mortar. 

The coping shall be formed of large fiat stones of such thickness as the 
engineer may direct, but in no case to be less than eight inches (8"). The 
upper surface of the coping shall be bush-hammered, and the joints and beds 
shall be dressed to one half an inch (£") throughout. Each stone must extend 
entirely across the wall when the wall is not more than four feet (4 ) thick. 

213. Rubble Masonry. For definitions connected with this 
class of masonry, see § 198. 

The stones used for rubble masonry should be prepared by 
simply knocking off all the weak angles of the block. It should be 
cleansed from dust, etc., and moistened, before being placed on its 
bed. This bed is prepared by spreading over the top of the lower 
course an ample quantity of good, ordinary-tempered mortar in 
which the stone is firmly embedded. The vertical joints should be 
carefully filled with mortar. The interstices between the larger 
masses of stone are filled by thrusting small fragments or chippings 
of stone into the mortar. In heavy walls of rubble masonry, the 
precaution should be observed to give the stones the same position 
in the masonry that they had in the quarry, i. e., to lay them on. 
their “ natural bed,” since stone offers more resistance to pressure 
in a direction perpendicular to the quarry-bed than in any other. 
The directions of the laminae in stratified stones show the position 
of the quarry-bed. 

To connect the parts well together and to strengthen the weak 
points, throughs or binders should be used in all the courses, and 
the angles should be constructed of cut or hammered stone. 

When carefully executed with good mortar, rubble possesses all the 
strength and durability required in structures of an ordinary char¬ 
acter, and is much less expensive than ashlar. Tile difficulty is m 
getting it well executed. The most common defects are (1) not bring¬ 
ing the stones to an even bearing; (2) leaving large vertical openings 
between the several stones; (3) laying up a considerable height of 
the wall dry, with only a little mortar on the face and back, and 
then pouring mortar on the top of the wall; (4) using insufficient 
cement, or that of a poor quality. The last defect is usually obviated 
by furnishing the cement to the contractor ; and the second and 
third defects may be detected by probing the vertical joints with a 
small steel rod. In order to secure good rubble, great skill and 



146 


STONE MASONRY. 


[CHAP. VII.. 


care are required on the part of the mason, and constant watchful¬ 
ness on the part of the inspector. 

A very stable wall can be built of rubble masonry without any 
dressing, except a draft on the quoins by which to plumb the cor¬ 
ners and carry them up neatly, and a few strokes of the hammer to 
spall off any projections or surplus stone. This style of work is 
not generally advisable, as very few mechanics can be relied upon to 
take the proper amount of care in leveling up the beds and filling 
the joints; and as a consequence, one small stone may jar loose and 
fall out, resulting probably in the downfall of a considerable part of 
the wall. Some of the naturally bedded stones are so smooth and 
uniform as to need no dressing or spalling up; a wall of such stones 
is very economical, since there is no expense of cutting and no time 
is lost in hunting for the right stone, and yet strong, massive work 
is assured. However, many of the naturally bedded stones have- 
inequalities on their surfaces, and in order to keep them level in the 
course it becomes necessary to raise one corner by placing spalls or 
chips of stone under the bed, and to fill the vacant spaces well and 
full with mortar. It is just here that the disadvantage of this style 
of work becomes apparent. Unless the mason places these spalls so 
that the stone rests firmly, i. e., does not rock, it will work loose, 
particularly if the structure is subject to shock, as the walls of 
cattle-guards, etc. Unless these spalls are also distributed so as to 
support all parts of the stone, it is liable to be broken by the weight 
above it. A few such instances in the same work may occasion con¬ 
siderable disaster. 

One of the tricks of masons is to put “ nigger-heads” (stones 
from which the natural rounded surface has not been taken off) 
into the interior of the wall. 

214. Bubble masonry is sometimes laid without any mortar, as 
in slope walls (§ 218), paving (§ 219), etc., in which case it is called 
dry rubble; but as such work is much more frequently designated 
as slope-wall masonry and stone-paving, it is better to reserve the 
term rubble for undressed stone laid in mortar. Occasionally box 
culverts are built of the so-called dry rubble; but as such construc¬ 
tion is not to be commended, there is no need of a term to desm- 
nate that kind of masonry. 

215. Amount of Mortar Required. If rubble masonry is com¬ 
posed of small and irregular stones, about one third of the mass 




BUBBLE MASONRY. 


14T 


will consist of mortar; if the stones are larger and more regular, 
one fifth to one quarter will he mortar. Laid in 1 to 2 mortar, 
ordinary rubble requires from one half to one barrel of cement per 
cubic yard of masonry. 

For the amount of cement and sand required for mortar of va¬ 
rious compositions, see the table on page 88. 

216. When Employed. Rubble masonry of the quality described 
above is frequently employed for the smallest sizes of bridge abut¬ 
ments, small arch culverts, box and open culverts, foundations of 
buildings, etc., and for backing for ashlar masonry (§ 200). 

217. Specifications for Rubble Masonry.* The following re¬ 
quirements, if properly complied with, will secure what is generally 
known among railroad engineers as superior rubble. 

Rubble masonry shall consist of coursed rubble of good quality laid in 
cement mortar. No stone shall be less than six inches (6") in thickness, unless 
otherwise directed by the engineer. No stone shall measure less than twelve 
inches (12") in its least horizontal dimension, or less than its thickness. At 
least one fourth of the stone in the face shall be headers, evenly distributed 
throughout the wall. The stones shall be roughly squared on joints, beds, and 
faces, laid so as to break joints and in full mortar beds. All vertical spaces 
shall be hushed with good cement mortar and then be packed full with spalls. 
No spalls will be allowed in the beds. Selected stones shall be used at all 
angles, and shall be neatly pitched to true lines and laid on hammer-dressed 
beds; draft lines may be required at the more prominent angles. 

The top of parapet walls, piers, and abutments shall be capped with stones 
extending entirely across the wall, and having a front and end projection of 
not less than four inches (4"). Coping stones shall be neatly squared, and laid 
with joints of less than one half inch (£"). The steps of wing-walls shall be 
capped with stone covering the entire step, and extending at least six inches 
(6") into the wall. Coping and step stones shall be roughly hammer-dressed 
on top, their outer faces pitched to true lines, and be of such thickness (not 
less than six inches) and have such projections as the engineer may direct. 

* ‘ The specifications for rubble masonry will apply to rabble masonry laid 
3ry, except as to the use of the mortar (see § 214).” 

218. Slope-wall Masonry. A slope-wall is a thin layer of 
masonry used to preserve the slopes of embankments, excavations, 
canals, river banks, etc., from rain, waves, weather, etc. The usual 
specifications are as follows:— 

The stones must reach entirely through the wall, and be not less than four 
inches (4") thick and twelve inches (12") long They must be laid with broken 
joints; and the joints must be as close and free from spalls as possible. 

* For complete specifications for masonry for various purposes, see Appendix L 







Ii8 


STOKE MASONRY. 


[CHAP. VII. 


219. Stone Paving. Stone paving is used for the inverts of arch 
culverts, for protecting the lower end of arches from undermining, 
and for foundations of box culverts and small arches. It is usually 
classed as dry rubble masonry, although it is occasionally laid with 
cement mortar. The usual specifications are about as follows : 

Stone paving shall be made of flat stones from eight inches (8") to fifteen 
inches (15'') in depth, set on edge, closely laid and well bedded in the soil, and 
shall present an even top surface. 

220. Riprap. Riprap is stone laid, without mortar, about the 
base of piers, abutments, etc., to prevent scour, and on banks to 
prevent wash. When used for the protection of piers, the stones 
are dumped in promiscuously, their size depending upon the 
material at hand and the velocity of the current; stones of 15 to 
25 cubic feet each are frequently employed. When used for the 
protection of banks, the riprap is laid by hand to a uniform thick¬ 
ness. 

221. Strength of Stone Masonry. The results obtained by 
testing small specimens of stone (see § 14) are useful in determin¬ 
ing the relative strength of different kinds of stone, but are of no 
value in determining the ultimate strength of the same stone when 
built into a masonry structure. The strength of a mass of masonry 
depends upon the strength of the stone, the size of the blocks, the 
accuracy of the dressing, the proportion of headers to stretchers, 
and the strength of the mortar. A variation in any one of these 
items may greatly change the strength of the masonry. 

The importance of the mortar as affecting the strength of 
masonry to resist direct compression is generally overlooked. The 
mortar acts as a cushion (§ 13) between the blocks of stone, and if 
it has insufficient strength it will be squeezed out laterally, pro¬ 
ducing a tensile strain in the stone; weak mortar thus causes the 
stone to fail by tension instead of by compression. No experiments 
have ever been made upon the strength of stone masonry under the 
conditions actually occurring in masonry structures, owing to the 
lack of a testing-machine of sufficient strength. Experiments 
made upon brick piers (§ 24G) 12 inches square and from 2 to 10 
feet high, laid in mortar composed of 1 volume Portland cement 
and 2 sand, show that the strength per square inch of the masonry 
is only about one sixth of the strength of the brick. An increase 
of 50 per cent, in the strength of the brick produced no appreciable 





STRENGTH OF STONE MASONRY. 


149 


effect on the strength of the masonry; but the substitution of 
cement mortar (1 Portland and 2 sand) for lime mortar (1 lime and 
3 sand) increased the strength of the masonry 70 per cent. The 
method of failure of these piers indicates that the mortar squeezed 
out of the joints and caused the brick to fail by tension. Since the 
mortar is the weakest element, the less mortar used the stronger the 
wall; therefore the thinner the joints and the larger the blocks, the 
stronger the masonry, provided the surfaces of the stones do not 
come in contact. 

It is generally stated that the working strain or stone masonry 
should not exceed one twentieth to one tenth of the strength of the 
stone; but it is clear, from the experiments on the brick piers re¬ 
ferred to above, that the strength of the masonry depends upon the 
strength of the stone only in a remote degree. In a general way it 
may be said that the results obtained by testing small cubes may 
vary 50 per cent, from each other (or say 25 per cent, from the 
mean) owing to undetected differences in the material, cutting, and 
manner of applying the pressure. Experiments also show that 
stones crack at about half of their ultimate crushing strength. 
Hence, when the greatest care possible is exercised in selecting and 
bedding the stone, the safe working strength of the stone alone 
should not be regarded as more than three eighths of the ultimate 
strength. A further allowance, depending upon the kind of struc¬ 
ture, the quality of mortar, the closeness of the joints, etc., should 
be made to insure safety. Experiments upon even comparatively 
large monoliths give but little indication of the strength of masonry. 
The only practicable way of determining the actual strength of 
masonry is to note the loads carried by existing structures. How¬ 
ever, this method of investigation will give only the load which does 
not crush the masonry, since probably no structure ever failed owing 
to the crushing of the masonry. After an extensive correspondence 
and a thorough search through engineering literature, the following 
list is given as showing the maximum pressure to which the several 
classes of masonry have been subjected. 

222. Pressure Allowed. Early builders used much more mas¬ 
sive masonry, proportional to the load to be carried, than is cus¬ 
tomary at present. Experience and experiments have shown that 
such great strength is unnecessary. The load on the monolithio 
piers supporting the large churches in Europe does not exceed 30 



150 


STONE MASONRY. 


[CHAP. YII c 


tons per sq. ft. (420 lbs. per sq. in.),* * * § or about one thirtieth of the 
ultimate strength of the stone alone. The stone-arch bridge of 140 
ft. span at Pont-y-Prydd, over the Taff, in Wales, erected in 1750, 
is supposed to have a pressure of 20.7 tons per sq. ft. (290 lbs. per 
. sq. in.) on hard limestone rubble masonry laid in lime mortar. A 
former bridge at the same place failed with 64 tons per sq. ft. 
Rennie subjected good hard limestone rubble in columns 4 feet 
square to 22 tons per sq. ft. (300 lbs. per sq. in.). f The granite piers 
of the Saltash Bridge sustain a pressure of 9 tons per sq. ft. (125 
lbs. per sq. in.). 

The maximum pressure on the granite masonry of the towers of 
the Brooklyn Bridge is about 28| tons per sq. ft. (about 400 lbs. per 
sq. in.). The maximum pressure on the limestone masonry of this 
bridge is about 10 tons per sq. ft. (125 lbs. per sq. in.). The face 
stones ranged in cubical contents from 14 to 5 cubic yards; the 
stones of the granite backing averaged about 1|- cu. yds., and of the 
limestone about 1J cu. yds. per piece. The mortar was 1 volume 
of Rosendale cement and 2 of sand. The stones were rougli-axed, 
or pointed to J-inch bed-joints and J-inch vertical face-joints. \ 
These towers are very fine examples of the mason’s art. 

In the Rookery Building, Chicago, granite columns about 3 feet 
square sustain 30 tons per sq. ft. without any signs of weakness. 

In the Washington Monument, Washington, D. C., the normal 
pressure on the lower joint of the walls of the shaft is 20.2 tons 
per sq. ft. (280 lbs. per sq. in.), and the maximum pressure brought 
upon any joint under the action of the wind is 25.4 tons per sq. ft. 
(350 lbs. per sq. in.).§ 

The pressure on the limestone piers of the St. Louis Bridge was, 
before completion, 38 tons per sq. ft. (527 lbs. per sq. in.); and after 
completion the pressure was 19 tons per sq. ft. (273 lbs. per sq. in.) 
on the piers and 15 tons per sq. ft. (198 lbs. per sq. in.) on the abut¬ 
ments. || 

The limestone masonry in the towers of the Niagara Suspension 


* In this connection it is convenient to remember that 1 ton per square foot is 
equivalent nearly to 14 (exactly 13.88) pounds per square inch. 

tProc. Inst, of C. E., vol. x. p. 241. 

X F. Collingwood, asst, engineer, in Trans. Am. Soc. of C. E. 

§ Report of Col. T. L. Casey, U. S. A., engineer in charge. 

| History of St. Louis Bridge, pp. 370-74. 




MEASUREMENT OF MASONRY. 


151 


Bridge failed under 36 tons per sq. ft., and were taken down,—how¬ 
ever, the masonry was not well executed. * 

At the South Street Bridge, Philadelphia, the pressure on the 
limestone rubble masonry in the pneumatic piles is 15.7 tons per 
sq. ft. (220 lbs. per sq., in.) at the bottom and 12 tons per sq. ft. at 
the top. “ This is unusually heavy, but there are no signs of weak¬ 
ness. The maximum pressure on the rubble masonry (laid in 
cement mortar) of some of the large masonry dams is from 11 to 14 
tons per sq. ft. (154 to 195 lbs. per sq. in.). The Quaker Bridge 
Dam is designed for a maximum pressure of 16f tons per sq. ft. 
(230 lbs. per sq. in.) on massive rubble masonry in best hydraulic 
cement mortar. \ 

223. Safe Pressure. In the light of the preceding examples 
it may be assumed that the safe load for the different classes of 
masonry is about as follows, provided each is the best of its class : 

Concrete.5 to 15 tons per square foot. 

Rubble,.10 to 15 “ “ 

Squared stone,.15 to 20 “ “ “ “ 

Limestone ashlar, . . . . 20 to 25 “ “ “ “ 

Granite ashlar,. 30 “ “ “ “ 

224. Measurement of Masonry. The method of determining 
the quantity of masonry in a structure is frequently governed by 
trade rules or local custom, and these vary greatly with locality. 
Masons have voluminous and arbitrary rules for the measurement 
of masonry; for example, the masons and stone-cutters of Boston 
at one time adopted a code of thirty-six complicated rules for the 
measurement of hammer-dressed granite. As an example of the 
indefiniteness and arbitrariness of all such rules, we quote the follow¬ 
ing, which are said to be customary in Pennsylvania: “ All open¬ 
ings less than 3 feet wide are counted solid. All openings more 
than 3 feet wide are taken out, but 18 inches is added to the 
running measurement for every jamb built. Arches are counted 
solid from the spring of the arch, and nothing allowed for arching. 
The corners of buildings are measured twice. Pillars less than 3 feet 
square are counted on three sides as lineal measurement, multiplied 
by the fourth side and depth; if more than 3 feet, the two opposite 

* Trans. Am. Soc. of C. E., vol. xvii. pp. 204-12. t Ibid., vol. vii. pp. 305-6. 

X Engineering News, vol. xix. p. 75. 











STONE MASONRY. 


[CHAP. YII. 


1 no 


sides are taken; to each side 18 inches for each jamb is added to 
lineal measurement thereof; the whole multiplied by the smaller side 
and multiplied by the depth.” 

A well-established custom has all the force of law, unless due 
notice is given to the contrary. The more definite, and therefore 
better, method is to measure the exact solid contents of the masonry, 
and pay accordingly. In “net measurement” all openings are de¬ 
ducted; in “gross measurement” no openings are deducted. 

The quantity of masonry is usually expressed in cubic yards. 
The perch is occasionally employed for this purpose; but since the 
supposed contents of a perch vary from 16 to 25 cubic feet, the term 
is very properly falling into disuse. The contents of a masonry 
structure are obtained by measuring to the neat lines of the design. 
If a wall is built thicker than specified, no allowance is made for the 
masonry outside of the limiting lines of the design; but if the 
masonry does not extend to the neat lines, a deduction is made for 
the amount it falls short. Of course a reasonable working allow¬ 
ance must be made when determining whether the dimensions of 
the masonry meet the specifications or not. 

In engineering construction it is a nearly uniform custom to 
measure all masonry in cubic yards; but in architectural construc¬ 
tion it is customary to measure water tables, string-courses, etc., 
by the lineal foot, and window-sills, lintels, etc., by the square foot. 
In engineering, all dressed or cut-stone work, such as copings, bridge 
seats, cornices, water-tables, etc., is paid for in cubic yards, with 
an additional price per square foot for the surfaces that are dressed, 
cut, or bush-hammered. 

225. Classification of Railroad Masonry. The stone masonry 
required in the construction of a railroad is usually classified about 
as follows: first-class masonry, second-class masonry, rubble masonry 
(sometimes called third-class masonry, § 209), rubble masonry laid 
dry (§ 214), stone paving, slope-walls, and riprap. First-class ma¬ 
sonry is equivalent to ashlar (§§ 200-7); this head generally includes 
bridge abutments and piers of the larger class, and arch culverts of 
greater span than 10 feet. Sometimes second-class masonry is speci¬ 
fied as squared-stone masonry (§§208-12), and sometimes as superior 
rubble (§§ 213-17); it is used in less important structures than first- 
class masonry. 

Fiequently specifications recognize also the following classifica- 




ESTIMATES OF COST. 


153 


tion : first-class arch masonry, second-class arch masonry, first-class 
bridge-pier masonry, second-class bridge-pier masonry, and pedestal 
masonry. The quality of work thus specified is the same as for first- 
class and second-class masonry respectively, the only difference 
being peculiar to the form of the masonry structure, as will be dis¬ 
cussed in succeeding chapters. The specifications for each structure 
should give the quantities of each kind of masonry. 

For complete specifications for railroad masonry, see Appendix I. 

226. Estimates of Cost of Masonry. The following estimates 
of the cost of masonry, from Trautwine’s Engineer’s Pocket-book ,* 
are pronounced by experts to be as accurate as such averages can 
be stated, since every item is liable to great variation. The estimates 
are based on the assumption that a mason receives $3.50 and a 
laborer $2.00 per day of 8 hours. 

227. “ Quarrying.f After the preliminary expenses of purchas¬ 
ing the site of a good quarry, cleaning off the surface earth and 
disintegrated top rock, and providing the necessary tools, trucks, 
cranes, etc., the total net expenses for getting out the rough stone 
for masonry ready for delivery may be roughly estimated thus: 
Stones of such size as two men can readily lift, measured in piles, 
will cost per cubic yard from J to \ the daily wages .of a quarry 
laborer. Large stones, ranging from | to 1 cubic yard each, got out 
by blasting, from 1 to 2 daily wages per cubic yard. Larger stones, 
ranging from 1 to IT cubic yards Cacli, in which most of the work 
must be done by wedges in order that the individual stones shall 
come out in tolerably regular shape and conform to stipulated dimen¬ 
sions, from 2 to 4 daily wages per cubic yard. The lower prices are 
low for sandstone, while the higher ones are high for granite. Under 
ordinary circumstances, about 1-^- cubic yards of good sandstone can 
be quarried at the same cost as 1 of granite—or, in other words, 
calling the cost of granite 1, that of sandstone will be f; hence the 
means of the foregoing limits may be regarded as rather full prices 
for sandstone, rather scant for granite, and about fair for limestone 
or marble. 

228. “ Dressing.}; In the first place, a liberal allowance should 
be made for waste. Even when the stone wedges out handsomely 
on all sides in large blocks of nearly the required shape and size. 


* Published by permission, 
t See Note 1, Appendix II. 

X See Notes 2 and 3, Appendix II. 









154 


STOKE MASONKY. 


[CHAP. VII. 


from £ to \ of the rough block will generally not more than cover 
waste of dressing. In moderate-sized blocks (say averaging about 
^ a cubic yard each) got out by blasting, from i to ^ will not be 
too much for stone of medium character as to straight splitting. 
The last allowance is about right for well-scabbled dressing. The 
smaller the stones the greater must be the allowance for waste. In 
large operations it becomes expedient to have the stones dressed, as 
far as possible, at the quarry, in order to diminish the cost of trans¬ 
portation, which, when the distance is great, constitutes an impor¬ 
tant item—especially when by land and on common roads. 

229. “ Ashlar. Average size of the stones, say 5 feet long, 2 
feet wide, and 1.4 feet thick—or two such stones to a cubic yard. 
Then, supposing the stone to be of granite or gneiss, the cost per 
cubic yard of ashlar facing will be : 

“ Getting out the stone from the quarry by blasting, allow¬ 
ing i for waste in dressing, 1£ cubic yards at $3.00 


per yard.$4 00 

Dressing 14 sq. ft. of face at 35 cents,.4 90 

Dressing 52 sq. ft. of beds and joints at 18 cents, ... 9 36 


Net cost of the dressed stone at the quarry, . . . $18 26 

Hauling (say 1 mile), loading, and unloading, .... 1 20 

Mortar, say,. 40 

Laying, including scaffold, hoisting machinery, etc., . 2 00 


Net cost, .$21 86 

Profit to contractor, say 15 per cent.,. 3 28 


Total cost per cubic }^ard,.$25 14 


“Dressing will cost more if‘the faces are to be rounded or 
moulded. If the stones are smaller than we have assumed, there 
will be more square feet per cubic yard to be dressed. If, in the 
foregoing case, the stones be perfectly well dressed on all sides, in¬ 
cluding the back, the cost per cubic yard would be increased about 
$10; and if some of the sides be curved, as in arch stones, say $12 
or $14; and if the blocks be carefully wedged out to given dimen¬ 
sions, $16 or $18. Under these conditions the net cost of the 
dressed stone at the quarry will be $28, $31, and $35 per cubic yard, 
respectively. 

‘ ‘ H ie stone be sandstone with good natural beds, the getting 
out may be put at $3.00 per cubic yard. Face dressing at 26 cents 












MARKET PRICE OF STONE. 


155 


pei sq, it., say 13.64 per cu. yd. Beds and joints at 13 cents per 
sq. it., say $6.76 per cu. yd. The total cost, then, is $19.55 instead 
of $25.14 for granite., and the net cost $17.00 instead of the $21.86 
per cu. yd. for granite. The total cost of large, well-scabbled, ranged 
sandstone masonry in mortar may be taken at about $10 per cu. yd. 

230. “ Rubble. With stones averaging about | cubic yard each, 
and common labor at $1 per day, the cost of granite rubble, such 
as is generally used as backing for the foregoing ashlar, will be about 
as follows : 

Getting out the stone from the quarry by blasting, allow¬ 
ing 4 for waste in scabbling, 1^ cu. yds. $3.00, . $3 43 

Hauling 1 mile, loading and unloading,.1 20 

Mortar (2 cu. ft., or 1.6 struck bushels of quicklime, and 
10 cu. ft. or 8 struck bushels of sand or gravel, and 


mixing),.1 50 

Scabbling, laying, scaffolding, hoisting machinery, etc., 2 50 


Net cost,.$8 63 

Profit to contractor, say 15 per cent.,.1 30 


Total cost per cubic yard,.$9 93 

< c Common mibble of small stones, the average size being such as 
two men can handle,* costs to get it out of the quarry about 80 cts. 
per yard of pile, or, to allow for waste, say $1.00. Hauling 1 mile, 
$1.00. It can be roughly scabbled and laid for $1.20 more. Mortar, 
as above, $1.50. Total net cost, $4.70; or with 15 per cent, profit, 
$5.40, at the above wages for labor.” 

231. Market Price of Stone. The average market quotations 
to builders and contractors for the year 1888 were about as follows, 
/. o. b. (free on board) at the quarry : 


Granite—rough. 

Limestone—common rubble, . 
“ good range rubble, 

“ bridge stone, . . 

“ dimension stone, . 

“ copings, . . . . 

Sandstone,. 


$0 40 to $0 50 per cubic foot. 

1 00 “ 1 50 per cubic yard. 

1 50 “ 2 00 “ 

08 “ 10 per cubic foot. 

25 “ 35 “ 

20 “ 35 “ 

35 “ 1 00 per cubic yard. 


232. Cost of Masonry.* TJ. S. Public Buildings. The following 
table gives the average contract price during the past few years for 
•cutting the stone for the United States government buildings :f 

* For additional data, see Notes 1-6, Appendix II, pages 544-46. 
f American Architect, vol. xxii. pp. 6, 7. 


c 


* 


i 

















156 


STONE MASONKY. 


[CHAP. VII. 


TABLE 15. 

Cost of Cutting Stone for U. S. Public Buildings. 


Kind of Surface. 

Granite. 

Marble. 

Limestone and 
Sandstone. 



Min. 

Max. 

Min. 

Max. 

Min. 

Max. 

Beds and joints, per sq. ft _ 

Pean-hammered, “ “ “ ... 
Plain fa.ce. 6-cut. “ “ "... 

$0 80 
45 

$0 35 
50 
65 

$0 20 
30 

$0 25 
35 

$0 12 
15 

$0 15 
20 

“ “ 8-cut, “ 

“ “ 10-cut, “ 

“ “ 12-cut, “ 

Rubbed, “ 

Tooled, “ 

tt it 


75 





it a 


88 





it a 


1 10 





t i a 



40 

20 

25 

tt <t 




50 

25 

30 






The following table shows the contract price for the masonry of 
the United States public buildings : 


TABLE 16. 


Cost of Masonry in U. S. Public Buildings. 


L 


Kind of Work. 


Random rubble, limestone. 

it it it 

tt t i tt 

“ “ sandstone. 

Squared masonry, sandstone. 

Coursed masonry, sandstone. 

Squared masonry, limestone. 

“ “ granite. 

Rock-face ashlar, “ . 

“ and cut-stoue granite, avg. 

Cut granite, basement and area walls. 

Rock-face ashlar, and cut and moulded trim¬ 
mings, Stony Point. Mich., sandstone.. 

Trimmings, Bedford limestone, bid. 

Rock-face ashlar, granite, retaining wall... 
Dressed coping, “ “ “ ... 

White sandstone,—furnished only. 

Armijo “ “ “ . 

Cut and moulded sandstone of superstructure 

‘ * average bid.... 

limestone, lowest bid. 

average bid. 

Rock-face ashlar, cut and moulded trim¬ 
mings, Middlesex brownstone. 

Cut and moulded, Bedford limestone. 

“ “ sandstone. 

“ limestone. 

“ sandstone. 

granite, superstructure.. 


fPLACE. 

Date. 

Cost 
per 
C u. Ft. 

Harrisburg, Va.... 

1885 

$0 20 

Cincinnati. O..... 

1884 

20 

Denver, Col. 

1883 

20 

Pittsburgh, Pa.. .. 

1886 

35 

ft a 

1885 

60 

a tt 

1885 

70 

Columbus, O. 

1884 

68 

Memphis, Tenn_ 

1886 

30 

Pittsburgh, Pa.... 

1886 

1 38 

it tt 

1886 

1 60 

ft tt 

1886 

2 00 

Fort Wayne, Ind.. 

1885 

1 52 

if ti tt 

1885 

1 65 

Memphis, Tenn. .. 

1886 

1 00 

<« < < 

1886 

2 50 

Dallas, Tex. 

1885 

35 

Denver, Col. 

1885 

73 

Council Bluffs, la. 

1885 

1 91 

ti tt ft 

1885 

2 12 

ii ft ft 

1885 

1 87 

it tt tt 

1885 

2 33 

Rochester, N. Y... 

1884 

2 41 

Louisville, Ky. 

1885 

2 00 

Dallas, Tex. 

1885 

2 46 

Hannibal, Mo. 

1885 

1 83 

Des Moines, la.... 

1887 

2 27 

Pittsburgh, Pa. 

1886 

3 00 

















































































ACTUAL COST. 


157 


233. Railroad Masonry. The following are the average prices 
actually paid in the construction of the Cincinnati Southern Rail¬ 
road, in 1873-77 :* 


First-class bridge masonry, per cu. yd.,.$10 39 

Second-class bridge masonry, in cement, per cu. yd., . 7 40 

Second-class bridge masonry, dry, per cu. yd., .... 7 02 

First-class arcb masonry, per cu. yd.,.11 24 

Second-class arcb masonry, in cement , per cu. yd., ... 8 61 

Second-class arch masonry, dry, per cu. yd.,.7 75 

Brick-work in tunnels, per cu. yd.,.8 50 

Brick-work in buildings, per cu. yd... 7 00 

Box-culvert masonry, in cement, per cu. yd.,.4 89 

Box-culvert masonry, dry, per cu. yd.,.4 32 

Concrete, per cu. yd., ..5 52 

Slope walls, per cu. yd.,.4 41 

Stone paving, per cu. yd...2 41 


234. Tunnel Masonry. The following are the average prices]* 
paid in 1883-87 on the new Croton Aqueduct tunnel which supplies 
New York City with water. The mortar was 2 sand to 1 Rosendale 

cement. 


Dimension-stone masonry (granite),.$42 50 

Brick-work lining, per cu. yd.,.10 14 

Brick-work backing, per cu. yd.,.8 49 

Rubble masonry, lining, per cu. yd.,.5 05 


Concrete lining, 3 stone to 1 Rosendale cement, percu.yd., 5 67 
Concrete lining, 5 stone to 1 Rosendale, per cu. yd., . . 5 16 
Concrete backing, 3 stone to 1 Rosendale, per cu. yd., . 4 73 

Concrete backing, 5 stone to 1 Rosendale, per cu. yd., . 4 22 

Fine-hammered face (6-cut) for cut stone, per sq. ft., . . 84 

Rough-pointed face for cut stone, per sq. ft., .... 50 

Additional for all kinds of masonry laid in Portland 

cement mortar, 2 to 1, per cu. yd.,.1 78 

Additional for all kinds of masonry laid in Rosendale 

cement mortar, 1 to 1, per cu. yd.,.1 20 

235. Bridge-pier Masonry. The following are the details of the 
cost, to the contractor, of heavy first-class limestone masonry for 
bridge-piers erected in 1887 by a prominent contracting firm : 


* Report of the Chief Engineer, December 1, 1877, Exhibit 3. 
f Report of the Commissioners, Table 4. 





















158 


STOKE MASOHRY. 


[CHAP. YII. 


Cost of stone (purchased),.$4 50 

Sand and cement,. 52 

Freight,.1 79 

Laying,.1 40 

Handling materials,. 65 

Derricks, tools, etc., . 40 

Superintendence, office expense, etc.,. 68 


Total cost per cubic yard,.$9 94 


The following data concerning the cost in 1887 of granite piers 
—two fifths cut-stone facing and three fifths rubble backing—are 
furnished by the same firm. The rock was very hard and tough. 


Facing :— 

Quarrying, including opening quarry,.$3 75 

Cutting to dimensions,.6 75 

Laying,.176 

Transportation 2 miles, superintendence, and general ex¬ 
penses, .2 05 


Total cost per cubic yard, .... ... $14 31 


Backing :— 

Quarrying,.$3 10 

Dressing,.3 60 

Laying, .1 75 

Sundries,.2 05 


Total cost per cubic yard,.$10 50 

The first-class limestone masonry in the piers of the bridges 
•across the Missouri at Plattsmouth (1879-80) cost the company 
$18.60 per cubic yard, exclusive of freight, engineering expenses, 
and tools.* The cost of first-class masonry in smaller piers usually 
ranges from $12 to $14 per cubic yard. 

At Chicago in 1887 the contract price for the masonry in bridge 
piers and abutments was about as follows : Concrete, 1 Portland 
cement, 3 sand, 6 broken stone, $9.00 per cu. yd.; concrete, 1 
natural cement, 3 sand, 5 broken stone, $6.00 per cu. yd.; stone 
facing and coping, $30.00 per cu. yd. 

236. Arch-culvert Masonry. The following are the details of 
the cost of the sandstone arch culvert (613 cu. yds.) at Nichols 
Hollow, on the Indianapolis, Decatur and Springfield Railroad, 


* Report of the Chief Engineer, Geo. S. Morison. 



























ACTUAL COST. 


159 


built in 1887. Scale of wages per day of 10 hours—foreman, 
$3.50 ; cutters, $3.00 ; mortar mixer, $1.50 ; laborer, $1.25 ; water- 
boy, 50 cents ; carpenters, $2.50. f 


TABLE 17. 

Actual Cost of Arch Masonry on Indianapolis, Decatur and Spring 

field Railroad. 


Items. 


Materials :— 

Stone—613 cn. yds. of sandstone $1 50.. 

Cement—130 bbls. German Portland $3 17 = $412 50 

40 “ English “ @ 3 25 = 130 00 

30 “ Louisville “ @ 96 = 28 75 

Sand—7 car-loads @ $5 50.. 

Total for materials.. 

Cutting :— 

Cutters and helpers. 

Templates, bevels, straight-edges, etc. 

Repairs of cutters’ tools. 

Water-boy . 

Total for cutting. 

Laying :— 

Masons, 110 days $3.50. 

Masons’ helpers. 

Mortar mixer. 

Water-boy. 

Arch centers, building and erecting. 

. Derrick, stone chute, etc. 

Laying track. 

Total for laying. 

Pointing . 

Grand Total : 

Total for labor. 

Total for materials. 

Total cost of masonry. 


Cost. 

Total. 

Per 
cu. yd. 

$919 50 

$1 50 

571 25 

94 

38 50 

06 

$1,529 25 

$2 50 

$1,370 48 

$2 24 

11 00 

01 

52 39 

09 

11 75 

02 

$1,445 62 

$2 36 

$384 87 

$0 63 

453 66 

74 

121 72 

20 

11 75 

02 

37 65 
14 63 

06 

02 

7 70 

01 

$1 032 08 

$1 68 

$30 00 

$0 05 

$2,507 60 

$4 09 

1,529 25 

2 50 

$4,036 85 

$6 59 


238. Summary of Cost. The following table, compiled from a 
large amount of data, will be convenient for hasty reference. Of 
course any such table must be used with caution, since such items 
are subject to great variation. 


f Data furnished by Edwin A. Hill, chief engineer. 






























































160 


STONE MASONRY, 


[CHAP. VII 


TABLE 18. 

Summary of Cost of Masonry. 


Description of Masonry. 


Arch masonry, first-class. 

Arch masonry, second-class (in cement). 

Box-culvert masonry, in cement. 

Brick masonry (see § 258). 

Bridge masonry, first-class. 

Bridge masonry, second-class (in cement) 

Concrete. 

Coping. 

Dimension-stone masonry, granite. 

Paving. 

Slope-wall masonry. 

Squared-stone masonry. 

Iiiprap. 

Rubble, first-class. 

Rubble, second-class (in cement). 


Cost per Cubic Yard. 

Min. 

Max. 

Average. 

$7 

00 

$12 

00 

$10 

00 

5 

00 

10 

00 

8 

00 

2 

50 

5 

00 

3 

50 

6 

00 

10 

00 

8 

00 

10 

00 

20 

00 

14 

00 

6 

00 

12 

00 

10 

00 

2 

50 

6 

00 

4 

00 

8 

00 

14 

00 

12 

00 

40 

00 

60 

00 

50 

00 

1 

00 

4 

00 

2 

00 

2 

00 

5 

00 

3 

00 

6 

00 

10 

00 

7 

00 

1 

00 

2 

50 

1 

50 

4 

00 

6 

00 

5 

00 

2 

00 

5 

00 

3 

00 






























CHAPTER YIIl. 

BRICK MASONRY. 

239. MORTAR. Lime mortar is generally employed for brick 
masonry, particularly in architectural constructions. Many of the 
leading railroads lay all brick masonry in cement mortar, and the 
practice should be followed more generally. The weakest part of 
a brick structure is the mortar. The primary purpose of the 
mortar is to form an adhesive substance between the bricks ; the 
second is to form a cushion to distribute the pressure uniformly 
over the surface. If the mortar is weaker than the brick, the 
ability of the masonry to resist direct compression is thereby con¬ 
siderably reduced. For the reason, see § 13; for the amount, see 
the Table 19, page 164. 

If the strains upon a wall were only those arising from a direct 
pressure, the strength of the mortar would in most cases be of 
comparatively little importance, for the crushing strength of aver¬ 
age quality mortar is far higher than the dead load which under 
•ordinary circumstances is put upon a wall; but, as a matter of fact, 
in buildings the load is rarely that of a direct crushing weight, 
other and more important strains being developed by the system of 
construction. Thus the roof tends to throw the walls out, the rafters 
being generally so arranged as to produce a considerable outward 
thrust against the wall. The action of the wind also produces aside 
strain which is practically of more importance than either of the 
others. In many cases the contents of a building exert an outward 
thrust upon the walls ; for example, barrels piled against the sides 
of a warehouse produce an outward pressure against the walls. 

In many brick constructions the use of cement mortar is abso¬ 
lutely necessary—as, for example, in tall chimneys, where the bear¬ 
ing is so small that great strength of the cementing material is 
required. 

240. The thickness of the mortar-joints should be about i to f 
of an inch. Thicker joints are very common, but should be avoided. 
If the bricks are even fairly good, the mortar is the weaker part of 

161 


162 


BRICK MASOKRY. 


[CHAP. VIII. 


the wall; hence the less mortar the better. Besides, a thin layer 
of mortar is stronger under compression than a thick one (see § 15).. 
The joints should be as thin as is consistent with their insuring a uni¬ 
form bearing and allowing rapid work in spreading the mortar. The 
joints of outside walls should be thin in order to decrease the dis¬ 
integration by weathering. The joints of inside walls are usually 
made from § to \ inch thick. 

Brick should not be merely laid , but every one should be rubbed 
and pressed down in such a manner as to force the mortar into the 
pores of the bricks and produce the maximum adhesion ; with quick¬ 
setting cement this is still more important than with lime mortar. 
For the best work it is specified that the brick shall be laid with a 
“ shove jointthat is, that the brick shall first be laid so as to 
project over the one below, and be pressed into the mortar, and 
then be shoved into its final position. 

Lime mortar is liable to work out of the joints, owing to the 
action of the elements and to changes of temperature. Hence it 
is customary either (1) to lay the face in mortar containing more 
lime than that used for the interior, or (2) to lay the 
face in a mortar containing more or less cement, or 
(3), in rare cases, to point the joints with neat cement 
mortar. Whatever the kind of mortar used, the finish 
of the face of the joint is important. The most 

Fig. 47. durable joint is finished as shown in Fig. 47, although, 
unfortunately for durability, it is customary to make the slope in 
the opposite direction. 

241. Since brick have great avidity for water, it is best to 
dampen them before laying. If the mortar is stiff and the brick 
dry, the latter absorb the water so rapidly that the mortar does 
not set properly, and will crumble in the fingers when dry. Neglect 
in this particular is the cause of most of the failures of brick-work. 
Since an excess of water in the brick can do no harm, it is best to 
thoroughly drench them with water before laying. Lime mortar is 
sometimes made very thin, so that the brick will not absorb all the 
water. This process interferes with the setting of the mortar, and 
particularly with the adhesion of the mortar to the brick. Watery 
mortar also contracts excessively in drying (if it ever does dry), 
which causes undue settlement and, possibly, cracks or distortion, 
Wetting the brick before laying will also remove the dust from the 
surface, which otherwise would prevent perfect adhesion. 








BOND. 


163 


242. Bond. The bricks used in a given wall being of uniform 
size are laid according to a uniform system, which is called the bond 
of the brick-work. As in ashlar masonry, so in brick-work, a header 
is a brick whose length lies perpendicular to the face of the wall; 
and a stretcher is one whose length lies parallel with the face. 
Brick should be made of such a size that two headers and a mortar- 
joint will occupy the same length as a stretcher. 

243. English Bond. This consists in laying entire courses of 

headers and stretchers, which some¬ 
times alternate, as in Fig. 48; but 
generally only one course of headers 
is laid for every two, three, four, etc., 
courses of stretchers. In ordinary 
practice the custom is to lay four to six 
courses of stretclibrs to one of head- 

The stretchers bind the walls 


X 


Fig. 48.—English Bond. 


ers. 


together lengthwise ; the headers, crosswise. The proportionate 
numbers of the courses of headers and stretchers should depend on 
the relative importance of transverse and longitudinal strength. 
The proportion of one course of headers to two of stretchers is that 
which gives equal tenacity to the wall lengthwise and crosswise. 

In building brick-work in English bond, it is to be borne in 
mind that there are twice as many vertical or side joints in a course 
of headers as there are in a course of stretchers; and that unless 
in laying the headers great care be taken to make these joints very 
thin, two headers will occupy a little more space than one stretcher, 
and the correct breaking of the joints—exactly a quarter of a brick—■ 
will be lost. This is often the case in carelessly built brick-work, in 
which at intervals vertical joints are seen nearly or exactly above 
each other in successive courses. 

244. Flemish Bond. This consists of a header and a stretcher 
alternately in each course, so placed 
that the outer end of each header ^ 
lies on the middle of a stretcher in -j 
the course below (Fig. 49). The □ 
number of vertical joints in each J 
course is the same, so that there is no J 
risk of the correct breaking of the ~ 
joints by a quarter of a brick being 
lost; 1 and the wall presents a neater appearance than one built in 


Fig. 49.— Flemish Bond. 


















































104 


BRICK MASONRY. 


[CHAP. YIII. 


English bond. The latter, however, when correctly built, is 
stronger and more stable than Flemish bond. 

245. Hoop-iron Bond. Pieces of hoop-iron are frequently laid 
flat in the bed-joints of brick-work to increase its longitudinal 
tenacity, about 2 inches of the ends of each piece being bent down 
and inserted into the vertical joints. Although thin strips of iron 
are generally employed, it would be better to use thicker pieces ; the 
value of the iron for this purpose depends wholly upon the rigidity 
of the ends which are turned down, and this will vary about as 
the square of the thickness. The strip of iron should be nearly 
as thick as the mortar-joint. This means of strengthening masonry 
is frequently employed over openings and to connect interior brick 
walls with stone fronts. 

246. Compressive Strength of Brick Masonry. Experi¬ 
ments at Watertowft, Mass., with the United States testing-machine, 
upon piers 12 inches square and from 1 ft. 4 in. to 10 ft. high, gave 
results as follows :* 


TABLE 19. 

Strength of Brick Masonry compared with that of the Brick and 

the Mortar. 


6 

Jz; 

Ed 

O 

S5 

Ed 

3 

Ed 

6. 

Ed 

03 

s' 

Composition op the Mortar. 

Number of Experiments. 

Ultimate Strength of the Pier, 

IN LBS. PER SQ. INCH. 

Strength of the Mortar (6-inch 
Cubes crushed between Steel) 
in lbs. per sq. in. Mean of 
three Trials. 

Strength of the 
Pier in terms 
of the Strength 
of the Brick. 

Strength of the Pier in Terms of 
the Strength of the Mortar. 

Min. 

Max. 

Mean. 

1 

1 lime, 3 sand. 

15 

1,508 

124 

.06 

.18 

.10 

12 

2 

2 mortar (1 lime, 3 sand), 1 Rosen- 









dale cement. 

1 

1,646 

183 



.11 

9 

3 

2 mortar (1 lime, 3 sand), 1 Port- 





land cement. 

1 

1,411 

192 



09 

7 

4 

1 Rosendale cement, 2 sand. 

1 

1,972 

162 



13 

12 

5 

1 Portland cement, 2 sand. 

8 

2,544 

545 

.10 

.27 

.17 

4.7 

a 

Clear Rosendale. 



521 





7 

Clear Portland cement. 

1 

2,375 

3,483 



.16 

0.7 







* Report on “ Tests of Metals, etc.,” for the year ending June 30,1884, pp. 69-122. 





































COMPRESSIVE STRENGTH. 


165 


The brick had an average strength of nearly 15,000 lbs. per sq. 
in., tested flatwise between steel. The mortar was 14^ months old 
when it was tested. The piers were built by a common mason, with 
•only ordinary care; and they were from a year and a half to two 
years old when tested. Their strength varied with their height; 
and in a general way the experiments show that the strength of a 
prism 10 ft. high, laid in either lime or cement mortar, is about two 
thirds that of a 1-foot cube. A deduction derived from so few 
■experiments (22 in all) is not, however, conclusive. The different 
lengths of the piers tested occurred in about equal numbers. The 
piers began to show cracks at one half to two thirds of their ultimate 
.strength. 

In attempting to draw conclusions from any experiments, it 
must be borne in mind continually that the result of a single trial 
may possibly be greatly in error. In this case this precaution is 
very important, since the difference between experiments apparently 
■exactly alike was in some cases as much as 50 per cent. A great 
variation in the results is characteristic of all experiments on stone, 
brick, mortar, etc. Except on the ground of a variation in ex¬ 
periments, it is difficult to explain why mortar No. 4 is weaker than 
No. 2, while the masonry is stronger ; or why the masonry of No. 5 
is stronger than that of No. 7. 

Of course the apparent efficiency of the masonry, as given in the 
table, depends upon the manner in which the strengths of the 
brick and mortar were determined, as well as upon the method of 
testing the masonry. For example, if the brick had been tested on 
end the apparent efficiency of the masonry would have been con¬ 
siderably more ; or if the mortar had been tested in thin sheets the 
strength of the masonry relative to that of the mortar would not 
have been so great.* * 

247. Some German experiments! gave results as in the table 

• _ _ _____—— 

* It should be mentioned that the mortar with which these piers were built appears 
to be much weaker than similar mortar under like conditions. (Compare page 72, 
and pages 126, 166,188,197 of the Report of Tests of Metals, etc., made at Watertown 
in 1884.) Ordinarily, mortar is eight to ten times as strong in compression as in 
tension, whereas the first six mortars in the preceding table were but little stronger 
in compression than such mortar should have been in tension. The officer in charge 
is “unable to offer any explanation. The cement was bought on the market; the 
maker’s name is not known. The cement was not tested.” However, the experi¬ 
ments are consistent with themselves, and therefore show relative strengths correctly. 

t Van Nostrand’s Engin’g Mag., vol. xxxiv. p. 240, from the Abstracts of the 
Inst, of C. E. (London), vol. 79, p. 376. 






166 


BRICK MASONRY. 


[CHAP. VIII. 


below. It is not stated how the strength of the brick or of the 
masonry was determined.* The term cement refers to Portland 
cement. According to the building regulations of Berlin, the safe 
load for brick masonry is one tenth of the results in the table. 

TABLE 20. 


Relative Strength of Brick and Brick Masonry. 


Kind of Brick. 

% 

Average Crush¬ 
ing Strength 
of Brick, in lbs. 
per sq. in. 

Ult t mate Strength, in lbs. per sq. in., of 1 
Brick-work with Mortar composed of— 

1 Lime, 

2 Sand. 

7 Lime, 

1 Cement, 
16 Sand. 

1 Cement, 
6 Sand. 

1 Cement,. 
3 Sand. 

Clinker stock. 

Selected “ . 

Ordinary “ . 

Perforated. 

Porous . 

Porous perforated. 

5,390 

3,669 

2,930 

2,759 

2,617 

1,195 

2,370 

1,620 

1,290 

1,210 

1,150 

530 

2,590 

1,760 

1,390 

1,320 

1,250 

570 

2,960 

2,020 

1,610 

1,520 

1,440 

650 

3,410 

2,320 

1,850 

1,710 

1,650 

750 


Both of the preceding series of experiments show conclusively 
that the strength of brick masonry is mainly dependent upon the 
strength of the mortar. An increase of 50 per cent, in the strength 
of the brick shows no appreciable effect on the strength of the ma¬ 
sonry. Notice., however, that the masonry in the fifth line of Table 
19 is 70 per cent, stronger than that in the first, due to the dif¬ 
ference between a good Portland cement mortar and the ordinary 
lime mortar. In the second table notice that brick laid in a 1 to 3 
Portland cement mortar is nearly 50 per cent, stronger than in a 1 
to 2 lime mortar. Similar experimentsf show that masonry laid in 
mortar composed of 1 part Rosendale cement and 2 parts sand is 56 
per cent, stronger than when laid in mortar composed of 1 part 
lime and 4 parts sand. A member of the Institute of Civil Engi¬ 
neers (London) saysj that brick-work laid in lime is only one fourth 
as strong as when laid in clear Portland cement. Probably the dif¬ 
ference in durability between cement mortar and lime mortar is 
considerably greater than their difference in strength. 

* If the strength of the brick (in any line of the table) be represented by 100, that 
of the masonry is 44, 48, 55, and 63, respectively, which shows that the values in the 
table were not derived directly from experiments. 

t Report of Experiments on Building Materials for the City of Philadelphia with 
the U. S. testing-machine at Watertown, Mass., pp. 32, 33. 

X Proc. Inst, of C. E., vol. xvii. p. 441. 



























I 


TRANSVERSE STRENGTH. 167 

248. Pressure allowed in Practice. The pressure at the base of 
a brick shot-tower in Baltimore, 246 feet high, is estimated at Or¬ 
tons per sq. ft. (about 90 lbs. per sq. in.). The pressure at the base 
of a brick chimney at Glasgow, Scotland, 468 ft. high, is estimated 
at 9 tons per sq. ft. (about 125 lbs. per sq. in.); and in heavy gales 
this is increased to 15 tons per sq. ft. (210 lbs. per sq. in.) on the 
leeward side. The leading Chicago architects allow 10 tons per sq. 
ft. (140 lbs. per sq. in.) on the best brick-work laid in 1 to 2 Port¬ 
land cement mortar ; 8 tons for good brick-work in 1 to 2 Rosendale 
cement mortar ; and 5 tons for ordinary brick-work in lime mortar. 
Ordinary brick piers have been known to bear 40 tons per sq. ft. 
(560 lbs. per sq. in.) for several days without any sign of failure. 

Tables 19 and 20 appear to show that present practice is very 
conservative with regard to the pressure allowed on brick masonry. 
According to Table 19 (page 164), the ultimate strength of the best 
brick laid in ordinary lime mortar is 110 tons per sq. ft.; if laid 
in 1 to 2 Portland cement mortar, 180 tons ; and by Table 20 (page 
166) the strength of ordinary brick in 1 to 2 lime mortar is 100 tons 
per sq. ft., and in 1 to 3 Portland cement mortar 140 tons. From 
the above, it would seem that reasonably good brick laid in good 
lime mortar should be safe under a pressure of 20 tons per sq. ft., 
and that the best brick in good Portland cement mortar should be safe 
under 30 tons per sq. ft. The nominal pressure allowed upon brick 
masonry depends upon the kind of materials employed; the degree of 
care with which it is executed ; whether it is for a temporary or per¬ 
manent, an important or unimportant structure ; and, it may be 
added, the care with which the nominal maximum load is estimated. 

249. Transverse Strength of Brick Masonry. Masonry is 
seldom employed where any strain except direct compression will 
come upon it, but sometimes it is subject to transverse strain. The 
transverse strength of brick-work depends theoretically upon the 
tensile strength of the brick and upon the adhesion and cohesion 
of the mortar, but practically the strength of the mortar deter¬ 
mines the strength of the masonry. For example, in the case of 
a high wall whose upper portion is overthrown by a lateral force or 
pressure of any kind, the failure is due either (1) to the breaking of 
the adhesion in the bed-joints and of the cohesion of the side-joints, 
or (2) to the rupture of the mortar in the bed-joints alone. The 
latter method of failure, however, is improbable, since the cohesion 





168 


BRICK MASONRY. 


[chap. vnr. 

of cement mortars is always much greater than their adhesion (com¬ 
pare §§ 134 and 137); and hence, in estimating the resistance of the 
wall to overturning, it becomes necessary to fix values for both the- 
cohesive and adhesive strength of the mortar at the time when the 
structure is first exposed to the action of the lateral force or pres¬ 
sure, and also to ascertain the relative areas of beds and side-joints 
in the assumed section of rupture. In good brick-work the aggre¬ 
gate area of the side-joints, in any section parallel to the beds, will 
amount to about one seventh of the total area of such section. 
Hence, when the masonry is liable to be subjected to transverse 
strains the adhesive strength of the mortar is more important than 
its cohesive strength. 

The adhesion of mortar to brick or stone has already been dis¬ 
cussed (§ 137). While the experiments uniformly show a relatively 
low adhesive power, it is well known that when old walls are de¬ 
molished the adhesion of even common lime mortar is found to be 
very considerable. Although the adhesive power of mortar may be 
small as compared with its tensile strength, good brick masonry has 
a considerable transverse strength. 

Experiments made under the author’s direction * indicate that 
brick beams bonded as regular masonry have a modulus of rupture 
equal to about twice the tensile strength of the mortar when built 
with ordinary care, and about three times when built with great care. 
When the beams are constructed as piers, i. e ., with no interlocking 
action, the modulus of rupture is about equal to the tensile strength 
of the mortar. 

250. Application. To illustrate the practical application of the 
fact that brick-work has a transverse strength, let it be required to 
compute the strain which may come upon a lintel, or girder used 
to support a brick wall over an opening, f 

Let H = the height, in feet, of the wall above the opening; 

H m = the height, in feet, of the wall that produces a maxi¬ 
mum strain on the lintel; 

H s = the height, in feet, of the masonry when it will just 
support itself over the opening ; 

S = the span, in feet; 
t = the thickness, in feet, of the wall; 

* The Technogeaph, University of Illinois, No. 7 (1892-93), pp. 29-37. 
fTho principle of the following computations is from an editorial in Engineering 
(London), vol. xiv. pp. 44 and 72. 






TRANSVERSE STRENGTH. 


169 


R = the modulus of rupture, in pounds per square inch, 
of the brick-work; 

W = the weight, in pounds, of a cubic foot of the wall. 
W varies from 100 to 140 pounds, and for conven¬ 
ience is here assumed to be 144; the error is always 
on the safe side. 

Consider the masonry as a beam fixed at both ends and loaded 
uniformly. Then, by the principles of the resistance of materials, 
when the masonry is just self-supporting, one twelfth of the weight 
of the wall above the opening multiplied by the span is equal to one 
sixth of the tensile strength multiplied by the thickness and also the 
square of the depth of the wall. The weight of the wall above the 
opening is W S H s t. Hence 

8H & f) 8 — \ (144 R) t H a * } . . . . (1) 

or 

' H - = m . 

Notice that the weight of the wall over any given opening in¬ 
creases as the height, while the resistance increases as the square of 
the height. The height for which the masonry is self-supporting 
is given by equation (2) ; for a height greater than H s the masonry 
would be more than self-supporting ; and for a height less than H s 
the masonry would need extraneous support. 

To find the relationship between the height of the wall that is 
self-supporting and the height that produces the maximum strain 
on the lintel, notice that, since the strength of the wall increases as 
H 2 and the weight as H, the net resistance of the wall increases as 
H. Consequently that portion of the wall which will be self-sup- 

jy 

porting can be represented by the —y part of the entire weight, and 

“s 

the part that must receive extraneous support can be represented 
H\ 

L-—) part of the entire weight. Since the weight of 

H S J 

the wall over a given opening varies as the height, the weight to be 

supported by the lintel is proportional to ^1 — JQf/; hence the 

greatest strain on the lintel will occur when the expression is a 
maximum,— i. e., when II m = ^Z/ s . 









170 


BRICK MASONRY. 


[CHAP. YIII. 


Substituting this value of II m in the above expression for the 

load on the lintel, ^1 — II, it becomes \ II S . This shows that 

the maximum load on the lintel is equal to one quarter of the weight 
of the self-supporting wall; or, since H m — \ H s , the maximum 
load on the girder is equal to one half of the weight of the entire 
wall above the opening. Substituting this value of H m in equation 
(2), we have 

*- = ts .< 3 > 


Hence it appears that the height of the wall producing the maxi- 

mum strain on the lintel will be equal to and that one half of 

4 K 

the wall will then be self-supporting and half will require extraneous 
support. Or, in other words, the greatest stress on a lintel due to 
a wall of any height will not be greater than that due to a distrib¬ 
uted load of 

\ WII m St = J WSt = nearly 18 pounds. . (4) 


251. Example*. To apply the above formula, assume that it is 
proposed to cut a 10-foot opening through an old brick wall, and 
that it is desirable to know whether the brick-work will be self-sup¬ 
porting, the wall rising 40 feet above the top of the opening. Sub¬ 
stituting the above data in equation (2) gives 


40 = 


00 )’ 

2 R 


or R = 1.25 lbs. per sq. in. 


Hence, to be self-supporting across the opening, the wall must be 
capable of supporting a tensile strain of 1.25 pounds per square 
inch. It would be poor lime mortar that would not bear eight or 
ten times this. Notice that if the wall were only 4 feet high over 
the opening, instead of 40 feet, as above, the strength required 
would be 12.5 pounds per square inch. 

For another illustration, assume that a brick wall 1 foot thick 
is to be built over a 10-foot opening, and that we wish to know 
whether a timber 10 inches deep and 12 inches wide will sustain the 
load. Assuming the beam as being fixed at the ends, the timber 
will sustain a uniformly distributed load of 10 tons with a deflection 










TRANSVERSE STRENGTH. 


171 


of one twelfth of an inch. This is equivalent to the entire weight 
of the wall when 14 feet high. If the wall is to be carried higher 
than this, the girder must he supported temporarily, or time must 
be given for the mortar to set. 

However, before the wall is 14 feet above the opening, the brick¬ 
work at the bottom will have attained some strength, and therefore 
the load on the girder will not he as great as above. The average 
strength of the brick-work will always be at least the average between 
the strength at the top and the bottom ; that is, the average strength 
will always be more than half of that at the bottom. Since 10 tons 
is the maximum load allowed on the girder, and since the maximum 
load which comes upon it is half of the entire weight of the masonry 
above the opening,* the timber will receive its maximum load when 
the wall is twice 14 feet, or 28 feet, above the opening. The masonry 
may be run up 28 feet without necessitating any extraneous support 
for the lintel, provided time enough is allowed for the mortar to 
develop the average tensile strength found by substituting in (4) 
the maximum load allowed on the girder, and solving for R. Mak¬ 
ing this substitution gives 

20000 = ^ , from which R = 0.90 lb. per sq. in. 

With an average strength of 0.90 lb. per sq. in., the wall will 
become self-supporting when 55 feet above the opening. 

252. Custom differs as to the manner of estimating the pressure 
on a girder due to a superincumbent mass of masonry. One extreme 
consists in assuming the masonry to be a fluid, and taking the load 
on the lintel as the weight of all the masonry above the opening. 
The opposite extreme consists in assuming the pressure to be the 
weight of the masonry included in a triangle of which the open¬ 
ing is the base and whose sides make 45° with this line. Both of 
these methods differ materially from the one discussed above ; and 
neither is defensible. As the wall is several days in building, the 
masonry first laid attains considerable strength before the wall is 
completed; and hence, owing to the cohesion of the mortar, the final 
weight on the girder can not be equal to or compared with any fluid 
volume. 

The principle involved in the second method would be applicable 


* See discussion of equation (3), above. 






172 


BRICK MASONRY. 


[CHAP. Yiir. 


to a wall composed wholly of perfectly smooth bricks. In a dry 
wall, the angle which the side lines make with the base would 
depend upon the bond and upon the relative length and breadth of 
the bricks. Assuming the boundary lines to make an angle of 45° 


3 R 

with the base the method gives a load ——- times that (§ 250) 

o 

which takes account of the transverse strength of the masonry, i . e., 
the frictional and tensile resistance of the wall. If R is relatively 
large and S is small, this fraction will be more than unity, under 
which conditions the second method is safe. But if R is small and 
S is large, then this fraction is less than one, which shows that 
under these conditions the second method is unsafe. 

The method of § 250 is quite simple and perfectly general. The 
substantial correctness of this method, illustrated in § 251, is 
proven by the fact that large openings are frequently cut through 
walls without providing any extraneous support; and also by the 
fact that walls are frequently supported over openings on timbers 
entirely inadequate to carry the load if the masonry did not have 
considerable strength as a beam. The discussion in § 251 also makes 
clear why frequently a temporary support is sufficient. After the 
masonry has been laid a short time, the strength of the mortar 
causes it to act as a beam. The discussion also shows the advantage 
of using cement mortar (or better, quick-setting cement mortar) 
when it is desired that the masonry shall early become self-sup¬ 
porting. 


253. Measurement of Brick-work. The method of determin¬ 
ing the quantity of brick masonry is governed by voluminous trade 
rules or by local customs, which are even more arbitrary than those 
for stone masonry (§ 224, which see). 

The quantity is often computed in perches, but there is no uni¬ 
formity of understanding as to the contents of a perch. It ranges 
from 16^ to 25 cubic feet. 

Brick-work is also often measured by the square rod of exterior 
surface. No wall is reckoned as being less than a brick and a half 
in thickness (13 or 13| inches), and if thicker the measurement is 
still expressed in square rods of this standard thickness. Unfor¬ 
tunately the dimensions adopted for a square rod are variable, the 
following values being more or less customary: 16J feet square or 






DATA FOR ESTIMATES. 


173 


272f square feet, 18 feet square or 324 square feet, and 16f square 
feet. 

The volume of a brick is sometimes used as a unit in stating the 
contents of a wall. The contents of the wall are found by multi¬ 
plying the number of cubic feet in the wall by the number of brick 
which it is assumed make a cubic foot; but as the dimensions of 
brick vary greatly (see § 62), this method is objectionable. A cubic 
foot is often assumed to contain 20 brick, and a cubic yard 600. 
The last two quantities are frequently used interchangeably, although 
the assumed volume of the cubic yard is thirty times that of the 
cubic foot. 

Brick-work is also sometimes measured by allowing a certain 
number of brick to each superficial foot, the. number varying with 
the thickness of the wall. A 4-inch wall (thickness = width of one 
brick) is frequently assumed to contain 7 bricks per sq. ft.; a 9-inch 
wall (thickness = width of two bricks), 14 bricks per sq. ft.; a 13- 
inch wall (thickness = width of three bricks), 21 bricks per sq. ft.* 
etc.; the number of brick per square foot of the face of the wall 
being seven times the thickness of the wall in terms of the width of 
a brick. 

254. The only relief from such arbitrary, uncertain, and indefi¬ 
nite customs is to specify that the masonry will be paid for by the 
cubic yard,—gross or net measurement, according to the structure 
or the preference of the engineer or architect. 

In engineering the uniform custom is to measure the exact solid 
contents of the wall. 

255. Data for Estimates. Number of Brick Required. Since 
the size of brick varies greatly (§ 62), it is impossible to state a rule 
which shall be equally accurate in all localities. If the brick be of 
standard size (8fx4x2f inches), and laid with |- to f-inch joints, 
a cubic yard of masonry will require about 410 brick; or a thousand 
brick will lay about 2J- cubic yards. If the joints are ±- to f-inch, a 
cubic yard of masonry will require about 495 brick; or a thousand 
brick will lay about 2 cubic yards. With face brick (8f X 4f X 2£ 
inches) and f-inch joints, a cubic yard of masonry will require about 
496 brick; or a thousand face brick will lay about 2 cubic yards. 

In making estimates for the number of bricks required, an al¬ 
lowance must be made for breakage, and for waste in cutting brick 
to fit angles, etc. With good brick, in massive work this allowance 



174 


BRICK MASONRY. 


[CHAP. Till. 


Heed not exceed 1 or 2 per cent.; but in buildings 3 to 5 per cent, 
is none too much. 

256. Amount of Mortar Required. The proportion of mortar 
to brick will vary with the size of the brick and with the thickness 
of the joints. With the standard size of brick (8^X4 x2^ inches), 
a cubic yard of masonry, laid with to f-inch joints, will require 
from 0.35 to 0.40 of a cubic yard of mortar; or a thousand brick 
will require 0.80 to 0.90 of a cubic yard. If the joints are J to f 
inch, a cubic yard of masonry will require from 0.25 to 0.30 of a 
cubic yard of mortar; or a thousand brick will require from 0.45 to 
0.55 of a cubic yard. If the joints are ^ of an inch, a cubic yard of 
masonry will require from 0.10 to 0.15 of a cubic yard of mortar; 
or a thousand brick will require from 0.15 to 0.20 of a cubic yard. 

With the above data, and the table on page 86, the amount of 
cement and sand required for a specified number of brick, or for a 
given number of yards of masonry, can readily be determined. 

257. Labor Required. “ A bricklayer, with a laborer to keep him 
supplied with materials, will lay on an average, in common house- 
walls, about 1,500 bricks per day of 10 working hours; in the neater 
outer faces of brick buildings, from 1,000 to 1,200; in good ordinary 
street fronts, from 800 to 1,000 ; and in the very finest lower-story 
faces used in street fronts, from 150 to 300 according to the number 
of angles, etc. In plain massive engineering work, he should aver¬ 
age about 2,000 bricks per day, or 4 cu. yds. of masonry; and in 
large arches, about 1,500, or 3 cu. yds.” * 

In the United States Government buildings the labor per thou¬ 
sand, including tools, etc., is estimated at seven eighths of the wages 
for ten hours of mason and helper. 

Table 21, opposite, f gives the actual labor, per cubic yard, re¬ 
quired on some large and important jobs. 

258. Cost. In the construction of the Cincinnati Southern R. R., 
during 1873-77, the brick lining of tunnels cost $8.50 per cu. yd.; 
brick-work in buildings, $7.00.]; The average price paid for the 
brick-work in the new Croton Aqueduct tunnel, which supplies New 
York City with water, was, including everything, $10.14 per cu. yd. 


* Trautwine’s Engineer’s Pocket-Book, p. 671. 
f Trans. Am. Soc. of C. E. 

X Report of the Chief Engineer, Dec. 1, 1877, Exhibit 3. 





SPECIFICATIONS. 


175 


TABLE 21. 

Labor required for Brick Masonry. 


Location and Description of the Masonry. 

Work required, n? 
Days per Cubic Yard 

High Bridge Enlargement, N. Y. City— 

~ Lining wall and flat arches laid with very close joints. 

0.714 

Washington (D. C.) Aqueduct— 

Circular conduit, 9 feet in diameter with walls 12 
inches thick. 

0.439 

St. Louis Water Works— 

Semi-circular conduit, 6 feet in diameter..... 

0.364 

New York City Storage Reservoir— 

Lining of gate-house walls and arches—rough work.. 

0.304 


for lining, and $8.49 for backing. The mortar was composed of 
1 part Rosendale natural cement and 2 parts of sand.* * * § 

In Chicago in 1887, the price of brick laid in lime in interior 
walls was about $11 per thousand, equivalent to about $7 per cu. yd. 
The wages of masons were from 45 to 50 cents per hour, and of 
common labor from 20 to 25 cents per hour. 

259. Specifications for Brick Masonry. For Buildings. 
There is not even a remote approach to uniformity in the specifica¬ 
tions for the brick-work of buildings. Ordinarily the specifications 
for the brick masonry are very brief and incomplete. The following 
conform closely to ordinary construction. Of course, a higher grade 
of workmanship can be obtained by more stringent specifications.! 

The brick in the exterior walls must be of good quality, hard-burned; fine, 
compact, and uniform in texture ; regular in shape, and uniform in size.f 
One fourth of the brick in the interior walls may be what is known as soft 
or salmon brick (see 2, § 56). The brick must be thoroughly wet before 
being laid. The joints of the exterior walls shall be from £ to f inch thick. § 
The joints of interior division-walls may be from f to i inch thick. The 
mortar shall be composed of 1 part of fresh, well-slaked lime and 2| to 3 parts 

* Report of the Aqueduct Commission, 1883-87, Table 4. 

t For specifications for masonry for various purposes, see Appendix I. 

\ See § 57, page 37. 

§ For the best work, omit this item and insert the following : The outside walls 
shall be faced with the best pressed brick of uniform color, laid in colored mortar , with 
joints not exceeding one eic/hth of an inch in thickness. Face brick are made a littl© 
larger (§ 62) than ordinary brick to compensate for the thinner joints. 














176 


BRICK MASONRY. 


[CHAP. VIII. 


of clean, sharp sand.* The lime-paste and the sand shall be thoroughly 
mixed before being used. The joints shall be well filled with the above 
•mortar ; no grout shall be used in the work. The bond must consist of five 
•courses of stretchers to one of headers, and shall be so arranged as to thor¬ 
oughly bind the exterior and interior portions of the wall to each other. 

The contractor must furnish, set up, and take away his own scaffolding; 
he must build in such strips, plugs, blocks, scantling, etc., as are required for 
securing the wood-work ; and must also assist in placing all iron-work, as 
beams, stairways, anchors, bed-plates, etc., connected with the brick-work. 

260. For Sewers. The following are the specifications employed, 
in 1885, in the construction of brick sewers in Washington, D. C. : 

“ The best quality of whole new brick, burned hard entirely through, free 
from injurious cracks, with true even faces, and with a crushing strength of 
not less than 5,000 pounds per square inch, shall be used, and must be thor¬ 
oughly wet by immersion immediately before laying. Every brick is required 
to be laid in full mortar joints, on bottom, sides, and ends, which for each 
brick is to be performed by one operation. In no case is the joint to be made 
by working in mortar after the brick has been laid. Every second course shall 
be laid with a line, and joints shall not exceed three eighths of an inch. The 
brick-work of the arches shall be properly bonded, and keyed as directed by 
the engineer. No portion of the brick-work shall be laid dry and afterwards 
grouted. 

“ The mortar shall be composed of cement and dry sand, in the proportion 
of 300 pounds of cement and 2 barrels of loose sand, thoroughly mixed dry, 
and a sufficient quantity of water afterwards added to form a rather stiff paste 
It shall be used within an hour after mixing, and not at all if once set. 

“The cement shall be of the best quality, freshly burned, and equal in 
every respect to the Round Top or Shepardstown cement, manufactured upon 
the formula of the engineer-commissioner of the District of Columbia, capable 
of being worked for twenty minutes in mortar without loss of strength, and 
shall be tested in such manner as the engineer may direct. After being mixed 
with water, allowed to set in air for twenty-four hours, and then immersed in 
water for six days, the tensile strength must be as follows : 


Neat cement.95 lbs. per sq. in. 

One part cement and one part sand.56 “ “ “ “ 

“ “ “ “ two parts “ .22 “ “ “ “ 

** “ “ “ three “ ** .12 “ “ “ ** 


‘The sand used shall be clean, sharp, free from loam, vegetable matter, or P 
other dirt, and capable of giving the above results with the cement. 

“ The water shall be fresh and clean, free from earth, dirt, or sewerage. 


* For masonry that is to be subjected to a heavy pressure, omit this item and 
insert the following : The mortar must be composed of 1 part lime-paste , 1 pari cement , 

and 2 parts of clean , sharp sand. Or, if a heavier pressure is to be resisted, specify 
that some particular grade of cement mortar is to be used. /See §§ 246 and 247.) 










SPECIFICATIONS. 


17 ? 


“ Tight mortar-boxes shall be provided by the contractor, and no mortar 
shall be made except in such boxes. 

“ The proportions given are intended to form a mortar in which every 
particle of sand shall be enveloped by the cement; and this result must be 
attained to the satisfaction of the engineer and under his direction. The 
thorough mixing and incorporation of all materials (preferably by machine 
labor) will be insisted upon. If by hand labor, the dry cement and sand shall 
be turned over with shovels by skilled workmen not less than six times before 
the water is added. After adding the water, the paste shall again be turned 
over and mixed with shovels by skilled workmen not less than three times be¬ 
fore it is used.” 

261. For Arches. The specifications for the brick arch masonry 
on the Atchison, Topeka and Santa Fe Railroad are as follows : 

“The bricks must be of the best quality of smooth, hard-burnt, paving 
bricks, well tempered and moulded, of the usual size, compact, well shaped, 
free from lime, cracks, and other imperfections, and must stand a pressure 
of 4,000 pounds per square inch without crushing. No bats will be allowed 
in the work except for making necessary closures. All bricks will be culled 
on the ground after delivery, and selected iu strict accordance with these 
specifications. 

“ The mortar must be made of 1 measure of good natural hydraulic cement 
and 2 measures of clean, sharp sand—or such other proportion as may be 
prescribed by the engineer—well mixed together with clean water, in clean 
mortar-beds constructed of boards, and must be used immediately after being 
mixed. 

“The brick must be laid flush in cement mortar, and must be thoroughly 
wet when laid. All joints and beds must be thoroughly filled with mortar so 
as to leave no empty spaces whatever in the masonry of the walls and arches, 
which must be solid throughout. The thickness of mortar-joints must be as 
follows : In the walls and in the arch between bricks of the same ring, not less 
than three eighths of an inch (|") nor more than one half inch ($■"). In the arch 
between rings, not less than one half inch (f') nor more than five eighths of 
an inch (f'). Each brick is to be driven into place by blows of a mallet. The 
bricks must be laid in the walls with the ordinary English bond, five stretcher 
courses to one header course. They must be laid in the arch in concentric 
rings, each longitudinal line of bricks breaking joints with the adjoining 
lines in the same ring and in the ring under it. No headers to be used in 
the arch.” 

262. Brick vs. Stone Masonry. Brick masonry is not much 
used, except in the walls of buildings, in lining tunnels, and in con¬ 
structing sewers, the general opinion being that brick-work is in 
every way inferior to stone masonry. This belief may have been 
well founded when brick was made wholly by hand, by inexpert 
operatives, and imperfectly burned in the old-time kilns, the prod- 



178 


BRICK MASONRY. 


[CHAP. VIII, 


uct being then generally poor ; but things have changed, and since 
the manufacture of brick has become a business conducted on a 
large scale by enterprising men, with the aid of a variety of machines 
and improved kilns, the product is more regular in size and quality 
and stronger than formerly. Brick is rapidly displacing stone for 
the largest and best buildings in the cities, particularly in Chicago 
and St. Petersburg, where the vicissitudes of the climate try masonry 
very severely. There are many engineering structures in which 
brick could be profitably employed instead of stone ; j,s, for example, 
the walls of box-culverts, cattle-guards, etc., and the less important 
bridge piers and abutments, particularly of highway bridges. 

Brick-work is superior to stone masonry in several respects, as 
follows : 1. In many localities brick is cheaper than stone, since 
the former can be made near by while the latter must be shipped. 
2. As brick can be laid by less skillful masons than stone, it costs 
less to lay it. 3. Brick is more easily handled than stone, and can 
be laid without any hoisting apparatus. 4. Brick requires less fit¬ 
ting at corners and openings. 5. Brick masonry is less liable to 
great weakness through inaccurate dressing or bedding. 6. Brick¬ 
work resists fire better than limestone, granite, or marble, sand¬ 
stone being the only variety of stone that can compare with brick 
in this respect. 7. Good brick stands the effect of weathering and 
of the acids in the atmosphere better than sandstones, and in dura¬ 
bility even approaches some of the harder stones (see §§ 31-33). 

8. All masonry fails when the mortar in its joints disintegrates or 
becomes dislodged; therefore brick masonry will endure the vicissi¬ 
tudes of the weather as well as stone masonry, or even better, since 
the former usually has thinner joints. 

Brick-work is not as strong as ashlar masonry, but costs less; 
while it is stronger and costs more than ordinary rubble. 

263. Brick Masonry Impervious to Water. It sometimes be¬ 
comes necessary to prevent the percolation of water through brick 
walls. A cheap and effective process has not yet been discovered, 
and many expensive trials have proved failures. The following 
account* gives the details of two experiments that were entirely suc¬ 
cessful. 

“ The face walls of the back bays of the gate-houses of the new 

* Abstract of a paper by Wm. L. Dearborn, in Trans. Am. Soc. of C. E., vol. i. 
pp. 20&-8- 







MASONRY IMPERVIOUS TO WATER. 


179 


Croton reservoir, located north of Eighty-sixth Street, in Central 
Park, New York City, were built of the best quality of hard-burnt 
brick, laid in mortar composed of hydraulic cement of New York 
[Ulster Co. Rosendale] and sand mixed in the proportion of one 
measure of cement to two of sand. The space between the walls was 
4 feet, and was filled with concrete. The face walls were laid up 
with great care, and every precaution was taken to have the joints 
well filled and to insure good work. The walls are 12 inches thick 
and 40 feet high; and the bays, when full, generally have 36 feet of 
water in them. 

“When the reservoir was first filled and the water let into the 
gate-houses, it was found to filter through these walls to a consider- 
able amount. As soon as this was discovered the water was drawn 
out of the bays, with the intention of attempting to remedy or pre¬ 
vent this infiltration. After carefully considering several modes of 
accomplishing the object desired, I [Dearborn] came to the conclm 
si on to try ‘ Sylvester’s Process for Repelling Moisture from Exter 
nal Walls.’ 

“ The process consists in using two washes or solutions for cov* 
ering the surface of the walls—one composed of Castile soap an(5 
water, and one of alum and water. The proportions are .three 
quarters of a pound of soap to one gallon of water, and half a pound 
of alum to four gallons of water, both substances to be perfectly 
dissolved in water before being used. The walls should be perfectly 
clean and dry, and the temperature of the air not below 50° Fahr.. 
when the compositions are applied. 

“ The first, or soap-wash, should be laid on, when boiling hot,, 
with a flat brush, taking care not to form a froth on the brick-wort. 
This wash should remain 24 hours, so as to become dry and hard 
before the second, or alum, wash is applied, which should be done 
in the same manner as the first. The temperature of this wash, 
when applied, maybe 60° or 70° Fahr.; and this also should remain 
24 hours before a second coat of the soap-wash is put on- 
These coats are to be applied alternately until the walls are made 
impervious to water. The alum and soap thus combined form an 
insoluble compound, filling the pores of the masonry and entirely 
preventing the water from entering the walls. 

“ Before applying these compositions to the walls' of the bays 
some 'experiments were made to test the absorption of water by 



180 


BRICK MASOHRY. 


[CHAP. YIIL 


bricks under pressure after being covered with these washes, in 
order to determine how many coats the walls would require to render 
them impervious to water. To do this, a strong wooden box large 
enough to hold two bricks was made, put together with screws, and 
in the top was inserted a 1-inch pipe 40 feet long. In this box 
were placed two bricks, after being made perfectly dry, which were 
then covered with a coat of each of the washes, as before directed, 
and weighed. They were then subjected to a column of water 40 
feet high ; and after remaining a sufficient length of time they were 
taken out and weighed again, to ascertain the amount of water they 
had absorbed. The bricks were then dried, and again coated with 
the washes and weighed, and subjected to pressure as before, this 
operation being repeated until the bricks were found not to absorb 
any water. Four coatings rendered the bricks impenetrable under 
the pressure of a 40-foot head. The mean weight of the bricks (dry) 
before being coated was 3|- lbs.; the mean absorption was one half- 
pound of water. A hydrometer was used in testing the solutions. 

“As this experiment was made in the fall and winter (1863), 
after the temporary roofs were put on to the gate-house, artificial 
heat had to be resorted to to dry the walls and keep the air at a 
proper temperature. The cost was 10 cents per sq. ft. As soon as 
the last coat had become hard, the water was let into the bays, and 
the walls were found to be perfectly impervious to water, and they 
remain so in 1870, after about 6|- years. 

264. “The brick arch of the footway of High Bridge is the arc 
of a circle, 29^ feet radius, and is 12 inches thick; the width on top 
is l 7 feet, and the length covered is 1,381 feet. The first two 
courses of the brick of the arch are composed of the best hard-burnt 
brick, laid edgewise in mortar composed of 1 part, by measure, of 
hydraulic cement of New York [Rosendale natural] and 2 parts of 
sand. The top of these bricks, and the inside of the granite 
ooping against which the two top courses of brick rest, was covered, 
when perfectly dry, with a coat of asphalt one half an inch thick, 
laid on when the asphalt was heated to a temperature of from 360° 
-to 518° Fahr. On top of this was laid a course of brick flatwise, 
dipped in asphalt, and laid when the asphalt was hot; and the joints 
were run full of hot asphalt. On top of this, a course of pressed 
brick was laid flatwise in hydraulic cement mortar, forming the 
paving and floor of the bridge. 




EFFLORESCENCE. 


181 


“ The area of the bridge covered with asphalted brick was 23,065 
sq, ft. There were used 94,200 lbs. of asphalt, 33 barrels of coal tar, 
10 cu. yds. of sand, and 93,800 bricks. The asphalt was the Trini¬ 
dad variety ; and was mixed with 10 per cent., by measure, of coal 
tar, and 25 per cent, of sand. The time occupied was 109 days of 
masons, and 148 days of laborers. Two masons and two laborers 
will melt and spread, of the first coat, 1,650 sq. ft. per day. The 
total cost of this coat was 5^ cents per sq. ft., exclusive of duty on 
asphalt. 

“ There were three grooves, 2 inches wide by 4 inches deep, 
made entirely across the brick arch immediately under the first 
coat of asphalt, thus dividing the arch into four equal parts. The 
grooves were filled with elastic paint cement. This arrangement 
was intended to guard against the evil effects of the contraction of 
the arch in winter ; for, since it was expected to yield slightly at 
these points and at no other, the elastic cement would prevent any 
leakage there. The entire experiment has proved p, very successful 
one, and the bridge has remained perfectly tight. 

“ In proposing the above plan for working the asphalt with the 
brick-work, the object was to avoid depending on a large continuous 
surface of asphalt, as is usual in covering arches, which very fre¬ 
quently cracks from the greater contraction of the asphalt than that 
of the masonry with which it is in contact, the extent of the asphalt 
on this work being only about one quarter of an inch to each brick. 
This is deemed to be an essential element in the success of the im¬ 
pervious covering.” 

265. Efflorescence. Masonry, particularly in moist climate 
or in damp places—as cellar walls,—is frequently disfigured by the 
formation of a white efflorescence on the surface. This deposit 
generally originates with the mortar, but frequently spreads over 
the entire face of the wall. The water which is absorbed by the 
mortar dissolves the salts of soda, potash, magnesia, etc., contained 
in the lime or cement, and on evaporating deposits these salts as a 
white efflorescence on the surface. With lime mortar the deposit 
is frequently very heavy, particularly on plastering; and, usually, 
it is heavier with natural than with Portland cement. The efflo¬ 
rescence sometimes originates in the brick, particularly if the brick 
was burned with sulphurous coal, or was made from clay contain¬ 
ing iron pyrites; and when the brick gets wet, the water dissolves 




182 


BRICK MASONRY. 


[CHAP. VIIL 


the sulphates of lime and magnesia, and on evaporating leaves the 1 
crystals of these salts on the surface. Frequently the efflorescence 
on the brick is due to the absorption by the brick of the impreg¬ 
nated water from the mortar. 

This efflorescence is objectionable because of the unsightly ap¬ 
pearance which it often produces, and also because the crystalliza¬ 
tion of these salts within the pores of the mortar and of the brick 
or stone causes disintegration which is in many respects like frost. 

As a preventive, Gillmore recommends* the addition of 100 lbs- 
of quicklime and 8 to 12 lbs. of any cheap animal fat to each barrel 
of cement. The lime is simply a vehicle for the fat, which should 
be thoroughly incorporated with the lime before slaking. The ob¬ 
ject of the fat is to saponify the alkaline salts. The method is not 
entirely satisfactory, since the deposit is only made less prominent 
and less effective, and not entirely removed or prevented. 

The efflorescence may be entirely prevented, whatever its origin, 
by applying Sylvester’s washes (see § 2G3) to the entire external sur¬ 
faces of the wall; and, since usually the efflorescence is due to the 
water absorbed by the mortar, it can generally be prevented, and 
can always be much diminished, by using mortar which is itself im¬ 
pervious to water (see § 141). The latter is the cheaper method, 
particularly if the impervious mortar be used only for the face of 
the joints. If the wall stands in damp ground, one or more of the 
horizontal joints just above the surface should be laid in impervious 
mortar, or better, the brick for several courses should be rendered 
impervious and be laid in impervious mortar to prevent the walks 
absorbing moisture from below. 


* “Limes, Hydraulic Cements, and Mortars,” p. 296. 





PART III. 


FOUNDATIONS. 


CHAPTER IX. 

INTRODUCTORY. 

26tT, DEFINITIONS. The term foundation is ordinarily used in¬ 
differently for either the lower courses of a structure of masonry or 
the artificial arrangement, whatever its character, on which these 
courses rest. For greater clearness, the term foundation will here 
be restricted to the artificial arrangement, whether timber or mason¬ 
ry, which supports the main structure ; and the prepared surface 
upon which this artificial structure rests will be called the bed of 
the foundation. There are many cases in which this distinction 
can not be adhered to strictly. 

267. Importance of the Subject. The foundation, whether 
for the more important buildings or for bridges and culverts, is the 
most critical part of a masonry structure. The failures of works of 
masonry due to faulty workmanship or to an insufficient thickness 
•of the walls are rare in comparison with those due to defective 
foundations. When it is necessary, as so frequently it is at the 
present day, to erect gigantic edifices—as high buildings or long- 
span bridges—on weak and treacherous soils, the highest construc¬ 
tive skill is required to supplement the weakness of the natural 
foundation by such artificial preparations as will enable it to sustain 
such massive and costly burdens with safety. 

Probably no branch of the engineer’s art requires more ability 
and skill than the construction of foundations. The conditions 
governing safety are generally capable of being calculated with 
as much practical accuracy in this as in any other part of a con- 

183 



184 


FOUNDATION'S: INTRODUCTORY. 


[CHAP. IS. 


struction ; but, unfortunately, practice is frequently based upon 
empirical rules rather than upon a scientific application of funda¬ 
mental principles. It is unpardonable that any liability to danger 
or loss should exist from the imperfect comprehension of a subject 
of such vital importance. Ability is required in determining the 
conditions of stability; and greater skill is required in fulfilling 
these conditions, that the cost of the foundation may not be pro¬ 
portionally too great. The safety of a structure may be imperiled, 
or its cost unduly increased, according as its foundations are laid 
with insufficient stability, or with provision for security greatly in 
excess of the requirements. The decision as to what general method 
of procedure will probably be best in any particular case is a ques¬ 
tion that can be decided with reasonable certainty only after long 
experience in this branch of engineering ; and after having decided 
upon the general method to be followed, there is room for the 
exercise of great skill in the means employed to secure the desired 
end. The experienced engineer, even with all the information 
which he can derive from the works of others, finds occasion for the 
use of all his knowledge and best common sense. 

The determination of the conditions necessary for stability can 
be reduced to the application of a few fundamental principles which 
may be studied from a text-book ; but the knowledge required to 
determine beforehand the method of construction best suited to the 
case in hand, together with its probable cost, comes only by personal 
experience and a careful study of the experiences of others. The 
object of Part III. is to classify the principles employed in con¬ 
structing foundations, and to give such brief accounts of actual 
practice as will illustrate the applications of these principles. 

268. Plan of Proposed Discussion. In a general way, soils 
may be divided into three classes : (1) ordinary soils, or those which 
are capable, either in their normal condition or after that condition 
has been modified by artificial means, of sustaining the load that is 
to be brought upon them ; (2) compressible soils, or those that are 
incapable of directly supporting the given pressure with any reason¬ 
able area of foundation ; and (3) semi-liquid soils, or those in which 
the fluidity is so great that they are incapable of supporting any 
considerable load. Each of the above classes gives rise to a special 
method of constructing a foundation. 

1. With a soil of the first class, the bearing power may be in- 




PLAN OF PROPOSED DISCUSSION. 


185 


creased by compacting the surface or by drainage ; or the area of 
the foundation may be increased by the use of masonry footing 
courses, inverted masonry arches, or one or more layers of timbers, 
railroad rails, iron beams, etc. Some one of these methods is or¬ 
dinarily employed in constructing foundations on land ; as, for 
example, for buildings, bridge abutments, sewers, etc. Usually all 
of these methods are inapplicable to bridge piers, i. e., for founda¬ 
tions under water, owing to the scouring action of the current and 
also to the obstruction of the channel by the greatly extended base 
of the foundation. 

2. With compressible soils, the area of contact may be increased 
by supporting the structure upon piles of wood or iron, which are 
sustained by the friction of the soil on their sides and 
pressure on the soil beneath their bases. This method is frequently 
employed for both buildings and bridges. 

3. A semi-fluid soil must generally be removed entirely and the 
structure founded upon a lower and more stable stratum. This 
method is specially applicable to foundations for bridge piers. 

There are many cases to which the above classification is not 
strictly applicable. 

For convenience in study, the construction of foundations will 
be discussed, in the three succeeding chapters, under the heads 
Ordinary Foundations , Pile Foundations, and Foundations lender 
Water. However, the methods employed in each class are not 
entirely distinct from those used in the others. 


by the direct 



CHAPTER X. 


ORDINARY FOUNDATIONS. 

269. In this chapter will be discussed the method of construct¬ 
ing the foundations for buildings, bridge abutments, culverts, or, 
in general, for any structure founded upon dry, or nearly dry, 
ground. This class of foundations could appropriately be called 
Foundations for Buildings, since these are the most numerous of the 
class. 

This chapter is divided into three articles. The first treats of 
the soil, and includes ( a) the methods of examining the site to de¬ 
termine the nature of the soil, (&) a discussion of the bearing power 
of different soils, and (c) the methods of increasing the bearing 
power of the soil. The second article treats of the method of de¬ 
signing the footing courses, and includes (a) the method of deter¬ 
mining the load to be supported, and ( b) the method of increasing 
the area of the foundation. The third contains a few remarks con¬ 
cerning the practical work of laying the foundation. 

Art. 1. The Soil. 

270. Examination of the Site. The nature of the soil to be 
built upon is evidently the first subject for consideration, and if it 
has not already been revealed to a considerable depth, by excava¬ 
tions for buildings, wells, etc., it will be necessary to make an ex¬ 
amination of the subsoil preparatory to deciding upon the details 
of the foundation. It will usually be sufficient, after having dug 
the foundation pits or trenches, to examine the soil with an iron 
rod or a post-auger from 3 to 5 feet further, the depth depending 
upon the nature of the soil, and the weight and importance of the 
intended structure. 

In soft soil, soundings 40 or 50 feet deep can be made by driving 
a small (say f-inch) gas-pipe with a hammer or maul from a tem¬ 
porary scaffold, the height of which will of course depend upon the 
length of the sections of the pipe. If samples of the soil are desired, 

186 


THE SOIL. 


187 


ART. 1.] 

use a 2-inch pipe open at the lower end. If much of this kind of 
work is to be done, it is advisable to fit up a hand pile-driving 
machine (see § 335), using a block of wood for the dropping weight. 
Borings 50 to 100 feet deep can be made very expeditiously in 
common soil or clay with a common wood-auger turned by men, 
with levers 2 or 3 feet long. The auger will bring up samples suf¬ 
ficient to determine the nature of the soil, but not its compactness, 
since it will probably be compressed somewhat in being cut off. 

When the testing must be made through sand or loose soil, it 
may be necessary to drive down an iron tube to prevent the soil 
from falling into the hole. The sand may be removed from the 
inside of the tube with an auger, or with the “ sand-pump” used in 
digging artesian wells. AVhen the subsoil is composed of various 
strata and the structure demands extraordinary precaution, borings 
must be made with the tools employed for boring artesian wells.* 

271. If the builder desires to avoid, on the one hand, the unnec¬ 
essarily costly foundations which are frequently constructed, or, on 
the other hand, those insufficient foundations evidences of which 
are often seen, it may be necessary, after opening the trenches, to 
determine the supporting power of the soil by applying a test load. 

In the case of the capitol at Albany, N. Y., the soil was tested 
by applying a measured load to a square foot and also to a square 
yard. The machine used was a mast of timber 12 inches square, 
held vertical by guys, with a cross-frame to hold the weights. For 
the smaller area, a hole 3 feet deep was dug in the blue clay at the 
bottom of the foundation, the hole being 18 inches square at the 
top and 14 inches at the bottom. Small stakes were driven into 
the ground in lines radiating from the center of the hole, the tops 
being brought exactly to the same level; then any change in the 
surface of the ground adjacent to the hole could readily be detected 
and measured by means of a straight-edge. The foot of the mast 
was placed in the hole, and weights applied. No change in the 
surface of the adjacent ground was observed until the load reached 
5.9 tons per sq. ft., when an uplift of the surrounding earth was 
noted in the form of a ring with an irregularly rounded surface, 
the contents of which, above the previous surface, measured 0.09 
cubic feet. Similar experiments were made by applying the load to 


* For illustrations of tools for this purpose, see Engineering News, vol. 21, p.3&4. 







188 


ORDINARY FOUNDATIONS. 


[CHAP. X. 


a square yard with essentially the same results. The several loads 
were allowed to remain for some time, and the settlements observed.* 

Similar experiments were made in connection with the construc¬ 
tion of the Congressional Library Building, Washington, D. C., with 
a frame which rested upon 4 foot-plates each a foot square. The 
frame could be moved from place to place on wheels, and the test 
was applied at a number of places. 

272. Bearing Power of Soils. It is scarcely necessary to say 
that soils vary greatly in their bearing power, ranging as they 
do from the condition of hardest rock, through all intermediate 
stages, to a soft or semi-liquid condition, as mud, silt, or marsh. 
The best method of determining the load which a specific soil will 
bear is by direct experiment (§ 271); but good judgment and ex¬ 
perience, aided by a careful study of the nature of the soil—its com¬ 
pactness and the amount of water contained in it—will enable one to 
determine, with reasonable accuracy, its probable supporting power. 
The following data are given to assist in forming an estimate of the 
load which may safely be imposed upon different soils. 

273. Rock. The ultimate crushing strength of stone, as deter¬ 
mined by crushing small cubes , ranges from 180 tons per square 
foot for the softest stone—such as are easily worn by running water 
or exposure to the weather—to 1,800 tons per square foot for the 
hardest stones (see page 11). The crushing strength of slabs, i. e ., 
of prisms of a less height than width, increases as the height de¬ 
creases. A prism one half as high as wide is about twice as strong 
as a cube of the same material. If a slab be conceived as being made 
up of a number of cubes placed side by side, it is easy to see why 
the slab is stronger than a cube. The exterior cubes prevent the 
detachment of the disk-like pieces (Fig. 1, page 6) from the sides of 
the interior cubes ; and hence the latter are greatly strengthened, 
which materially increases the strength of the slab. In testing 
cubes and slabs the pressure is applied uniformly over the entire, 
upper surface of the test specimen ; and, reasoning from analogy, 
it seems probable that when the pressure is applied to only a small 
part of the surface, as in the case of foundations on rock, the strength 
will be much greater than that of cubes of the same material. 

The table on page 190 contains the results of experiments made 


* W. J. McAlpine, the engineer in charge, in Trans. Am. Soc. C. E., vol. ii. p- 287. 






A-RT. 1.] 


THE SOIL. 


189 > 


by the author, and shows conclusively that a unit of material has a 
much greater power of resistance when it forms a portion of a larger 
mass than when isolated in the manner customary in making ex¬ 
periments on crushing strength. 

The ordinary “crushing strength” given in next to the last 
column of Table 22 was obtained by crushing cubes of the identical 
materials employed in the other experiments. The concentrated 
pressure was applied by means of a hardened steel die thirty-eight 
sixty-fourths of an inch in diameter (area = 0.277 sq. in.). All the 
tests were made between self-adjusting parallel plates of a hydro¬ 
static testing-machine. No packing was used in either series of 
experiments ; that is to say, the pressed surfaces were the same in 
both series. However, the block of limestone 7 inches thick (Ex¬ 
periments Nos. 8 and 13) is an exception in this respect. This 
block had been sawed out and was slightly hollow, and it was 
thought not to be worth while to dress it down to a plane. As pre¬ 
dicted before making the test, the block split each time in the di¬ 
rection of the hollow. If the bed had been flat, the block would 
doubtless have shown a greater strength. The concentrated pres¬ 
sure was generally applied near the corner of a large block, and 
hence the distance from the center of the die to the edge of the 
block is to the nearest edge. Frequently the block had a ragged 
edge, and therefore these distances are only approximate. The 
quantity in the last column—“Ratio”—is the crushing load per 
square inch for concentrated pressures divided by the crushing load 
per square inch for uniform pressure. 

The experiments are tabulated in an order intended to show that 
the strength under concentrated pressure varies (1) with the thick¬ 
ness of the block and (2) with the distance between the die and 
the edge of the material being tested. It is clear that the strength 
increases very rapidly with both the thickness and the distance from 
the edge to the point where the pressure is applied. Therefore we 
conclude that the compressive strength of cubes of a stone gives 
little or no idea of the ultimate resistance of the same material when 
in thick and extensive layers in its native bed. 

274. The safe bearing power of rock is certainly not less than 
one tenth of the ultimate crushing strength of cubes ; that is to say, 
the safe bearing power of solid rock is not less than 18 tons per sq. 
ft. for the softest rock and 180 for the strongest. It is safe to say 



190 


ORDINARY FOUNDATIONS. 


[CHAP. X. 


TABLE 22. 

Compressive Strength when the Pressure is applied on only a Part 

v of the Upper Surface. 


o 

$5 

63 

O 

ic 

W 

« 

E 

63 

Ph 

Material. 

Thickness of Block. 

_ 

Center of Die from 

Edge. 

No. of Trials. 

Crushing Strength 

per Square Inch 

—Concentrated 

Pressure. 

---—-- 

No. of Trials. 

Crushing Strength 

per Square Inch- 

Distributed Pres¬ 

sure. 

Ratio. 

1 

Lime Mortar. 


h in - 

2 in. 

4 

3,610 

3 

1,340 

2.7 

2 

Marble. 

1 

4 4 

2 

4 4 

4 

18,050 

3 

10,500 

1.7 

3 

4 4 

2 

4 » 

2 

4 4 

3 

36,100 

3 

10,100 

3.6 

4 

Brick. 

24 “ 

2 

44 

11 

11,801 

13 

2,654 

5.1 

5 

Limestone.. 

3 

4 < 

2 

4 4 

4 

31,046 

3 

3,453 

9.0 

6 

Sandstone. 

3 

4 4 

2 

44 

2 

51,600 

3 

3,696 

14.0 

7 

Limestone. 

4 

44 

2 

44 

3 

75,361 

2 

4,671 

16.0 

8 

( 4 

7 

4 4 

2 

4 4 

2 

64,077 

5 

3,453 

18.5 

6 

Sandstone . 

3 

4 4 

2 

4 4 

2 

51,600 

3 

3,696 

14.0 

9 

4 c 

3 

4 4 

3 

4 4 

1 

59,204 

6 4 

4 4 

16.0 

10 

4 4 

3 

4 4 

4 

4 4 

1 

75,810 

4 4 

4 4 

20.5 

7 

Limestone . 

4 

44 

2 

4 4 

3 

75,361 

2 

4,761 

16.0 

11 

4 4 

4 

4 4 

3 

4 4 

3 

102,900 

4 4 

44 

22.0 

12 

4 4 

4 

4 4 

4 

4 4 

1 

111,188 

4 4 

4 4 

24.0 

8 

4 4 

7 

4 4 

2 

4 4 

2 

64,077 

5 

3,453 

18.5 

13 

4 4 

7 

4 4 

4 

4 4 

1 

87,720 

4 4 

4 4 

25.0 


14 


Clay, which for years has safely carried, without appreciable settlement, 
buildings concentrating 1^ to 2 tons per square foot (20 to 28 pounds 
per square inch), when tested in the form of cubes was crushed with 4 
to 8 pounds per square inch. In this case the average “ ratio” is 4.3. 


that almost any rock, from the hardness of granite to that of a soft 
crumbling stone easily worn by exposure to the weather or to run¬ 
ning water, when well bedded will bear the heaviest load that can 
be brought upon it by any masonry construction. 

It scarcely ever occurs in practice that rock is loaded with the 
full amount of weight which it is capable of sustaining, as the extent 
of base necessary for the stability of the structure is generally suffi¬ 
cient to prevent any undue pressure coming on the rock beneath. 

275. Clay. The clay soils vary from slate or shale, which will 
support any load that can come upon it, to a soft, damp clay which 
will squeeze out in every direction when a moderately heavy pres- 


















































ART. 1.] 


191 


THE SOIL. 


sure is brought upon it. Foundations on clay should be laid at 
such depths as to be unaffected by the weather ; since clay, at even 
considerable depths, will gain and lose considerable water as the 
seasons change. The bearing power of clayey soils can be very 
much improved by drainage (§ 285), or by preventing the penetra¬ 
tion of water. If the foundation is laid upon undrained clay, care 
must be taken that excavations made in the immediate vicinity do 
not allow the clay under pressure to escape by oozing away from 
under the building. When the clay occurs in strata not horizontal, 
great care is necessary to prevent this flow of the soil. When coarse 
sand or gravel is mixed with the clay, its supporting power is greatly 
increased, being greater in proportion as the quantity of these 
materials is greater. When they are present to such an extent that 
the clay is just sufficient to bind them together, the combination 
will bear as heavy loads as the softer rocks. 

276. The following data on the bearing power of clay will be of 
assistance in deciding upon the load that may safely be imposed 
upon any particular clayey soil. From the experiments made in 
connection with the construction of the capitol at Albany, N. Y., 
as described in § 271, the conclusion was drawn that the extreme 
supporting power of that soil was less than 6 tons per sq. ft., and 
that the load which might be safely imposed upon it was 2 tons per 
sq. ft. “ The soil was blue clay containing from 60 to 90 per cent, 
of alumina, the remainder being fine siliceous sand. The soil con¬ 
tains from 27 to 43, usually about 40, per cent, of water ; and vari¬ 
ous samples of it weighed from 81 to 101 lbs. per cu. ft. ” In the 
case of the Congressional Library (§ 271), the ultimate supporting 
power of “yellow clay mixed with sand ” was 13| tons per sq. ft.; 
and the safe load was assumed to be 2£ tons per sq. ft. Experi¬ 
ments made on the clay under the piers of the bridge across the 
Missouri at Bismarck, with surfaces 1J inches square, gave an aver¬ 
age ultimate bearing power of 15 tons per sq. ft.* 

The stiffer varieties of what is ordinarily called clay, when kept 
dry, will safely bear from 4 to 6 tons per sq. ft.; but the same clay, 
if allowed to become saturated with water, can not be trusted to 
bear more than 2 tons per sq. ft. At Chicago, the load ordinarily 
put on a thin layer of clay (hard above and soft below, resting on a 


* Report of the engineer, Geo. S. Morison. 






192 


ORDINARY FOUNDATIONS. 


[CHAP. X. 


thick stratum of quicksand) is 1J to 2 tons per sq. ft.; and the set¬ 
tlement, which usually reaches a maximum in a year, is about 1 
inch per ton of load. Experience in central Illinois shows that, if 
the foundation is carried down below the action of frost, the clay 
subsoil will bear 1^ to 2 tons per sq. ft. without appreciable settling. 
Eankine gives the safe load for compressible soils as I^ to If tons 
per sq. ft. 

277. Sand. The sandy soils vary from coarse gravel to fine sand. 
The former when of sufficient thickness forms one of the firmest 
■and best foundations ; and the latter when saturated with water 
is practically a liquid. Sand when dry, or wet sand when prevented 
from spreading laterally, forms one of the best beds for a founda¬ 
tion. Porous, sandy soils are, as a rule, unaffected by stagnant 
water, but are easily removed by running water ; in the former case 
they present no difficulty, but in the latter they require extreme 
care at the hands of the constructor, as will be considered later. 

278. Compact gravel or clean sand, in beds of considerable 
thickness, protected from being carried away by water, may be 
loaded with 8 to 10 tons per sq. ft. with safety. In an experiment 
in France, clean river-sand compacted in a trench supported 100 
tons per sq. ft. Sand well cemented with clay and compacted, if 
protected from water, will safely carry 4 to G tons per sq. ft. 

The piers of the Cincinnati Suspension Bridge are founded on a 
bed of coarse gravel 12 feet below low-water, although solid lime¬ 
stone was only 12 feet deeper ; if the friction on the sides of the 
pier* be disregarded, the maximum pressure on the gravel is 4 tons 
per sq. ft. The piers of the Brooklyn Suspension Bridge are founded 
44 feet below the bed of the river, upon a layer of sand 2 feet thick 
resting upon bed-rock ; the maximum pressure is about tons 
per sq. ft. 

At Chicago sand and gravel about 15 feet below the surface are 
successfully loaded with 2 to 2J tons per sq. ft. At Berlin the safe 
load for sandy soil is generally taken at 2 to 24 tons per sq. ft. The 
Washington Monument, Washington, B. C., rests upon a bed of 
very ^fine sand two feet thick underlying a bed of gravel and bowl¬ 
ders; the ordinary pressure on certain parts of the foundation is 
not far from 11 tons per sq. ft., which the wind may increase to 
nearly 14 tons per sq. ft. 


* For the amount of such friction, see §§ 418-19 and § 455. 







ART. 1.] 


THE SOIL. 


193 


279. Semi-Liquid Soils. With a soil of this class, as mud, silt, 
or quicksand, it is customary (1) to remove it entirely, or (2) to 
sink piles, tubes, or caissons through it to a solid substratum, or 
\'d) to consolidate the soil by adding sand, earth, stone, etc. The 
method of performing these operations will be described later. Soils 
•of a soft or semi-liquid character should never be relied upon for a 
foundation when anything better can be obtained ; but a heavy 
■superstructure may be supported by the upward pressure of a seini- 
nquid soil, in the same way that water bears up a floating body. 

According to Rankine,* a building will be supported when the 


pressure at its base is w hi- S ! n ~ 
r VI — sin 

pression w is the w T eight of a unit volume of the soil, h is the depth 



of immersion, and a is the angle of repose of the soil. If a — 5°, 
then according to the preceding relation the supporting power of 
the soil is 1.4 w h per unit of area ; if a = 10°, it is 2.0 w h ; and 


if a — 15°, it is 2.9 iv h. The weight of soils of this class, i. e., 


mud, silt, and quicksand, varies from 100 to 130 lbs. per cu. ft. 
Rankine gives this formula as being applicable to any soil; but since 
it takes no account of cohesion, for most soils it is only roughly ap¬ 
proximate, and gives results too small. The following experiment 
seems to show that the error is considerable. “ A 10-foot square 
base of concrete resting on mud, whose angle of repose w T as 5 to 1 
{a =11J°], bore 700 lbs. per sq. ft.”f This is 2J times the result 
by the above formula, using the maximum value of w. 

Large buildings have been securely founded on quicksand by 
making the base of the immersed part as large and at the same time 
as light as possible. Timber in successive layers (§ 309) or grillage 
on piles (§ 320) is generally used in such cases. This class of foun¬ 
dations is frequently required in constructing sewers in water-bear¬ 
ing sands, and though apparently presenting no difficulties, such 
foundations often demand great skill and ability. 

280. It is difficult to give results of the safe bearing power of 
soils of this class. A considerable part of the supporting power is 
derived from the friction on the vertical sides of the foundation ; 
hence the bearing power depends in part upon the area of the side 
surface in contact with the soil. Furthermore, it is difficult to de- 


* See Rankine’s Civil Engineering, p. 379. 
t Proc. Inst, of C. E., vol. xviii. p. 493. 





ORDINARY FOUNDATIONS. 


rCHAP. X. 


termine the exact supporting power of a plastic soil, since a consid¬ 
erable settlement is certain to take place with the lanse of time. 
The experience at New Orleans with alluvial soil and a jW experi¬ 
ments* that have been made on quicksand seem to indicate luat 
with a load of £ to 1 ton per square foot the settlement will not be 
excessive. 

281. Bearing Power: Summary. Gathering together the results 
of the preceding discussion, we have the following table • 


TABLE 23. 

Safe Bearing Power of Soils. 


Kind of Material. 

Safe Bear 
in Tons pj 

Min. 

TNG Power 
er Sq. Ft. 

Max. 

Rock—the hardest—in thick layers, in native bed (§ 274) 

•200 

_ 

“ equal to best ashlar masonry (§ 274). 

25 

30 

“ “ “ “ brick “ “ . 

15 

20 

“ “ “ poor “ “ “ . 

5 

10 

Clay, in thick beds, always dry (§ 276). 

4 

6 

“ “ “ “ moderately dry (§ 276). 

2 

4 

" soft (§ 276). 

1 

2 

Gravel and coarse sand, well cemented (§ 278). 

8 

10 

Sand, compact and well cemented, “ . 

4 

6 

“ clean, dry. “ . 

2 

4 

Quicksand, alluvial soils, etc. (§ 280). 

0.5 

1 


282. Conclusion. It is well to notice that there are some prac¬ 
tical considerations that modify the pressure which may safely be 
put upon a soil. For example, the pressure on the foundation of 
a tall chimney should be considerably less than that of the low mas¬ 
sive foundation of a fire-proof vault. In the former case a slight 
inequality of bearing power, and consequent unequal settling, might 
endanger the stability of the structure ; while in the latter no seri¬ 
ous harm would result. The pressure per unit of area should be 
less for a light structure subject to the passage of heavy loads—as, 

* Trans. Am. Soc. of C. E., vol. xiy. p. 182 ; Engineering, vol. xx. p. 103; Proc. 
Inst, of C. E., vol. xvii. p. 443; Cleeman’s Railroad Practice, pp. 103-4. 





























ART. 1.] 


THE SOIL. 


195 


for example, a railroad viaduct—than for a heavy structure subject 
only to a quiescent load, since the shock and jar of the moving load 
are far more serious than the heavier quiescent load. 

The determination of the safe bearing power of soils, particular¬ 
ly when dealing with those of a semi-liquid character, is not the 
only question that must receive careful attention. In the founda¬ 
tions for buildings, it may be necessary to provide a safeguard 
against the soil's escaping by being pressed out laterally into excava¬ 
tions in the vicinity. In the foundations for bridge abutments, it 
maybe necessary to consider what the effect will be if the soil around 
the abutment becomes thoroughly saturated with water, as it may 
during a flood; or what the effect will be if the soil is deprived of 
its lateral support by the washing away of the soil adjacent to the 
abutment. The provision to prevent the wash and undermining 
action of the stream is often a very considerable part of the cost of 
the structure. The prevention of either of these liabilities is a prob¬ 
lem by itself, to the solution of which any general discussion will 
contribute but little. 

283. Improving the Bearing Power of the Soil. When 
the soil directly under a proposed structure is incapable, in its nor 
mal state, of sustaining the load that will be brought upon it, the 
bearing power may be increased (1) by increasing the depth of the 
foundation, (2) by draining the site, (3) by compacting the soil, or 
(4) by adding a layer of sand. 

284. Increasing the Depth. The simplest method of increas¬ 
ing the bearing power is to dig deeper. Ordinary soils will bear 
more weight the greater the depth reached, owing to their becom¬ 
ing more condensed from the superincumbent weight. Depth is 
especially important with clay, since it is then less liable to be dis¬ 
placed laterally owing to other excavations in the immediate vicin¬ 
ity, and also because at greater depths the amount of moisture in it 
will not varv so much. 

In any soil, the bed of the foundation should be below the reach 
of frost. Even a foundation on bed-rock should be below the frost 
line, else water may get under the foundation through fissures, and, 
freezing, do damage. 

285. Drainage. Another simple method of increasing the bear¬ 
ing power of a soil is to drain it. The water may find its way to 
the bed of the foundation down the side of the wall, or by pereola- 



196 


ORDINARY FOUNDATIONS. 


[CHAP. X. 


tion through the soil, or through a seam of sand. In most cases 
the bed can be sufficiently drained by covering it with a layer of 
gravel—the thickness depending upon the plasticity of the soil,— 
■and then surrounding the building with a tile-drain laid a little 
below the foundation. In extreme cases, it is necessary to enclose 
the entire site with a puddle-wall to cut off drainage water from a 
higher area. 

286. Springs. In laying foundations, springs are often met 
with, and sometimes prove very troublesome. The water may be 
excluded from the foundation pit by driving sheet piles, or by plug¬ 
ging the spring with concrete. If the flow is so strong as to wash 
the cement out before it has set, a heavy canvas covered with pitch, 
etc., upon which the concrete is deposited, is sometimes used ; or 
the water may be carried away in temporary channels, until the 

concrete in the artificial bed shall have set, when the water-wavs 

* 

may be filled with semi-fluid cement mortar. Below is an account 
of the method of stopping a very troublesome spring encountered 
in laying the foundation of the dry-dock at the Brooklyn Navy 
Yard. 

“The dock is a basin composed of stone masonry resting on 
piles. The foundation is 42 feet below the surface of the ground 
and 37 feet below mean tide. In digging the pit for the founda¬ 
tion, springs of fresh water were discovered near the bottom, which 
proved to be very troublesome. The upward pressure of the water 
was so great as to raise the foundation, however heavily it was loaded. 
The first indication of undermining by these springs was thesettling 
of the piles of the dock near by. In a day it made a cavity in which 
a pole was run down 20 feet below the foundation timbers. Into 
this hole were thrown 150 cubic feet of stone, which settled 10 feet 
during the night; and 50 cubic feet more, thrown in the following 
day, drove the spring to another place, where it burst through a 
bed of concrete 2 feet thick. This new cavity was filled with 
concrete, but the precaution was taken of putting in a tube so as to 
permit the water to escape ; still it burst through, and the opera¬ 
tion was repeated several times, until it finally broke out through a 
heavy body of cement 14 feet distant. In this place it undermined 
the foundation piles. These were then driven deeper by means of 
followers; and a space of 1,000 square feet around the spring was 
then planked, forming a floor on which was laid a layer of brick in 



ART. 1.] 


THE SOIL. 


197 


dry cement, and on that a layer of brick set in mortar, and the 
foundation was completed over all. Several vent-holes were left 
through the floor and the foundation for the escape of the water. 
The work was completed in 1851, and has stood well ever since .” * 

287. Consolidating the Soil. A soft, clayey soil can be greatly 
improved by spreading a thin layer of sand, dry earth, or broken 
stone over the bed of the foundation and pounding it into the soil. 
If the soil is very soft, compacting the surface will be insufficient; 
in this case the soil may be consolidated to a considerable depth by 
driving short piles into it. For this purpose small piles—say 6 
feet long and 6 inches in diameter—serve better than large ones ; 
and they can be driven with a hand-maul or by dropping a heavy 
block of wood with a tackle attached to any simple frame, or by a 
hand pile-driver (§ 335). They may be driven as close together as 
necessary, although 2 to 4 feet in the clear is usually sufficient. 
The latter method of compacting the soil is far more efficient than 
pounding the surface. In the case of impact upon earth, the im¬ 
mediate layers are compressed at once, and by their inertia and 
adhesion to the surrounding soil they intercept the effect of the 
blow, and thus prevent the consolidation of the lower strata. Even 
though the effect of a blow is not communicated to any considerable 
depth, the heavy masses of masonry make themselves felt at great 
depth, and hence for heavy buildings it is necessary to consolidate 
the lower strata. This can be done most easily and most efficiently 
by driving piles (see Art. 2). 

In this connection it is necessary to remember that clay is com¬ 
pressible, while sand is not. Hence this method of consolidating 
soils is not applicable to sand, and is not very efficient in soils 
largely composed of it. 

288. Sand Piles. Experiments show that in compacting the 
yoil by driving piles, it is better to withdraw them and immediately 
fill the holes with sand, than to allow the wooden piles to remain. 
This advantage is independent of the question of the durability of 
the wood. When the wooden pile is driven, it compresses the soil 
an amount nearly or quite equal to the volume of the pile, and 
when the latter is withdrawn this consolidation remains, at least 
temporarily. If the hole is immediately filled with sand this com- 

* Delafield's Foundations in Compressible Soils, p. 14—a pamphlet published to 
the Engineer’s Department of the U. S. Army. 






198 


ORDINARY FOUNDATIONS. 


[CHAP. X.. 


pression is retained permanently, and the consolidation may be still 
farther increased by ramming the sand in in thin layers, owing to- 
the ability of the latter to transmit pressure laterally. And further, 
the sand pile will support a greater load than the wooden pile; for, 
since the sand acts like innumerable small arches reaching from 
one side of the hole to the other, more of the load is transmitted to 
the soil on the sides of the hole. To secure the best results, the 
sand should be fine, sharp, clean, and of uniform size. 

289. When the piles are driven primarily to compact the soil, 
it is customary to load them and also the soil between them, either 
by cutting the piles otf near the surface and laying a tight platform 
of timber on top of them (see § 320), or by depositing a bed of con¬ 
crete between and over the heads of the piles (see § 319). 

If the soil is very soft or composed largely of sand, this method 
is ineffective; in which case long piles are driven as close together 
as is necessary, the supporting power being derived either from the 
resting of the piles upon a harder substratum or from the buoyancy 
due to immersion in the semi-liquid soil. This method of securing 
a foundation by driving long piles is very expensive, and is seldom 
resorted to for buildings, since it is generally more economical to 
increase the area of the foundation. 

290. Layers of Sand. If the soil is very soft, it may be ex¬ 
cavated and replaced by sand. The method of using sand for piles 
has been described in § 288, which see. The opportunities for the 
use of sand in foundations are numerous, and the employment of 
it would, in many constructions, promote economy and stability. 
The simplest method of using sand for this purpose is to excavate 
a trench or pit to the proper depth, and fill it by depositing succes¬ 
sive layers of sand, each of which should be thoroughly settled by 
a heavy beetle before laying the next. To cause the sand to pack 
firmly, it should be slightly moistened before being placed in the 
trench. 

Sand, when used in this way, possesses the valuable property of 
assuming a new position of equilibrium and stability should the 
soil on which it is laid yield at any of its points ; not only does this 
take place along the base of the sand bed, but also along its edges 
or sides. The bed of sand must be thick enough to distribute the 
pressure on its upper surface over the entire base. There is no way 
of telling what this thickness should be, except by trial. 




ART. 2.] 


DESIGNING THE FOOTING. 


199 


291. The following examples, cited by Trautwine,* are interest¬ 
ing as showing the surprising effect of even a thin layer of sand 
or gravel : 

“Some portions of the circular brick aqueduct for supplying 
Boston with water gave a great deal of trouble when its trenches 
passed through running quicksands and other treacherous soils. 
Concrete was tried, but the wet quicksand mixed itself with it and 
hilled it. AYooden cradles, etc., also failed ; and the difficulty was 
overcome by simply depositing in the trenches about two feet in 
depth of strong gravel. 

“Smeaton mentions a stone bridge built upon a natural bed of 
gravel only about 2 feet thick, overlying deep mud so soft that an 
iron bar 40 feet long sank to the head by its own weight. Although 
a wretched precedent for bridge building, this example illustrates 
the bearing power of a thick layer of well-compacted gravel.” 


Art. 2. Designing the Footing. 

292. Load to be Supported. The first step is to ascertain the 
load to be supported by the foundation. This load consists of three 
parts : (1) the building itself, (2) the movable loads on the floors 
and the snow on the roof, and (3) the part of the load that may be 
transferred from one part of the foundation to the other by the 
force of the wind. 

/ 293. The weight of the building is easily ascertained by calcu¬ 
lating the cubical contents of all the various materials in the struct¬ 
ure. If the weight is not equally distributed, care must be taken 
to ascertain the proportion to be carried by each part of the foun¬ 
dation. For example, if one vertical section of the wall is to con¬ 
tain a number of large windows while another will consist entirely 
of solid masonry, it is evident that the pressure on the foundation 
under the first section will be less than that under the second. 

In this connection it must be borne in mind that concentrated 
pressures are not transmitted, undiminished, through a solid mass 
in the line of application, but spread out in successively radiating 
lines ; hence, if any considerable distance intervenes between the 
foundation and the point of application of this concentrated load, 


* Engineer’s Pocket-book (ed. 1885), p. 634. 






200 


ORDINARY FOUNDATIONS. 


[CHAP. X. 


the pressure will be nearly or quite uniformly distributed over the 
entire area of the base. The exact distribution of the pressure can 
not be computed. 

The following data will be useful in determining the weight of 
the structure * 


TABLE 24. 
Weight of Masonry. 


Kind of Masonry. 


Weight 

in 

LBS. PER CO. FT 


Brick-work, pressed brick, thin joints. 

“ ordinary quality. 

“ soft brick, thick joints. 

Concrete, 1 cement, 3 sand, and 6 broken stone. 

Granite—6 per cent, more than the corresponding limestone_ 

Limestone, ashlar, largest blocks and thinnest joints. 

“ “ 12" to 20" courses and f- to |-inch joints. 

“ squared-stone (see § 208). 

“ rubble, best. 

“ “ rough. 

Mortar, 1 Rosendale cement and 2 sand. 

“ common lime, dried. 


145 

125 

100 

14b 

160 

155 

148 

142 

136 

116 

100 


Sandstone—14 per cent, less than the corresponding limestone.. 


Ordinary lathing and plastering weighs about 10 lbs. per sq. ft. 
The weight of floors is approximately 10 lbs. per sq. ft. for dwell¬ 
ings ; 25 lbs. per sq. ft. for public buildings; and 40 or 50 lbs. per 
sq. ft. for warehouses. The weight of the roof varies with the kind 
of covering, the span, etc. A shingle roof may be taken at 10 lbs. 
per sq. ft., and a roof covered with slate or corrugated iron at 25 
lbs. per sq. ft. 

294. The movable load on the floor depends upon the nature of 
the building. For dwellings, it does not exceed 10 lbs. per sq. ft.; 
for large office buildings, it is usually taken at 30 lbs. per sq. ft.; 
for churches, theatres, etc., the maximum load—a crowd of people 
—may reach 100 lbs. per sq. ft.; for stores, warehouses, factories. 
























ART. 2.] 


DESIGNING THE FOOTING. 


201 


etc., the load will be from 100 to 400 lbs. per sq. ft., according to 
the purposes for which they are used. 

The preceding loads are the ones to be used in determining the 
strength of the floor, and not in designing the footings; for there 
is no probability that each and every square foot of floor will have 
its maximum load at the same time. The amount of moving load 
to be assigned in any particular case is a matter of judgment. At 
Chicago in designing tall steel-skeleton office buildings, it is the 
practice to assume that nearly all of the maximum live load reaches 
the girders, that a smaller per cent, reaches the columns, and that 
no live load reaches the footings. In many cities the building law 
specifies the live load to be assumed as reaching the footing. 

Attention must he given to the manner in which the weight of 
the roof and floors is transferred to the walls. For example, if the 
floor joists of a warehouse run from back to front, it is evident that 
the back and front walls alone will carry the weight of the floors 
and of the goods placed upon them, and this will make the pressure 
upon the foundation under them considerably greater than under 
the other walls. Again, if a stone-front is to be carried on an arch 
or on a girder having its bearings on piers at each side of the build¬ 
ing, it is manifest that the weight of the whole superincumbent 
structure, instead of being distributed equally on the foundation 
under the front, will be concentrated on that part of the founda¬ 
tion immediately under the piers. 

295. The pressure of the wind against towers, tall chimneys, 
etc., will cause a concentration of the weight of the structure upon 
one side of the foundation. The maximum horizontal pressure of 
the wind is usually taken as 50 lbs. per sq. ft. on a flat surface per¬ 
pendicular to the wind, and on a cylinder at about 30 lbs. per sq. 
ft. of the projection of the surface. The pressure upon an inclined 
surface, as a roof, is about 1 lb. per sq. ft. per degree of inclination 
to the horizontal. For example, if the roof has an inclination of 
30° with the horizontal, the pressure of the wind will he about 30 
lbs. per sq. ft. 

The effect of the wind will be considered in §§ 301-4. 

296. Area Required. Having determined the pressure which 
may safely be brought upon the soil, and having ascertained the 
weight of each part of the structure, the area required for the foun¬ 
dation is easily determined by dividing the latter by the former. 



202 


ORDINARY FOUNDATION'S 


[CHAP. A. 


Tlien, having found the area of foundation, the base of the struct¬ 
ure must be extended by footings of masonry, concrete, timber, 
etc., so as to (1) cover that area and (2) distribute the pressure uni¬ 
formly over it. The two items will be considered in inverse order. 

297. Center of Pressure and Center of Base. In construct¬ 
ing a foundation the object is not so much to secure an absolutely 
unyielding base as to secure one that will settle as little as possible, 
and uniformly. All soils will yield somewhat under the pressure of 
any building, and even masonry itself is compressed by the weight 
of the load above it. The pressure per square foot should, there¬ 
fore, be the same for all parts of the building, and particularly of 
the foundation, so that the settlement may be uniform. This can 
be secured only when the axis of the load (a vertical line through 
the center of gravity of the weight) passes through the center of 
the area of the foundation. If the axis of pressure does not coincide 
exactly with the axis of the base, the ground will yield most on the 
side which is pressed most; and as the ground yields, the base as¬ 
sumes an inclined position, and carries the lower part of the struct¬ 
ure with it, thus producing unsightly cracks, if nothing more. 

The coincidence of the axis of pressure with the axis of resist¬ 
ance is of first importance. This principle is self-evident, and yet 
the neglect to observe it is the most frequent cause of failure in the 
foundations of buildings. 

Fig. 50 is an example of the way in which this principle is 

violated. The shaded portion 
represents a heavily loaded exte¬ 
rior wall, and the light portion a 
lightly loaded interior wall. The 
foundations of the two walls are 
rigidly connected together at 
• .•.* •;:;;*• • their intersection. The center 

• *• * v * ■‘• v*-;of the load is under the shaded 

fig. so. section, and the center of the 

area is at some point farther to the left ; consequently the exterior 
wall is caused to incline outward, producing cracks at or near the 
corners of the building. Doubtless the two foundations are con¬ 
nected in the belief that an increase of the bearing surface is of first 
importance; but the true principle is that the coincidence of the 
axis of pressure with the axis of resistance is the most important. 











ART. 2.] 


DESIGNING THE FOOTING. 


203 


Fig. 51 is another illustration of the same principle. The foun¬ 
dation is continuous under the opening, 
and hence the center of the foundation is to 
the left of the center of pressure; conse¬ 
quently the wall inclines to the right, pro¬ 
ducing cracks, usually over the opening.* 

298. The center of the load can be made 
to fall inside of the center of foundation by 
extending the footings outwards, or by cur¬ 
tailing the foundations on the inside. The 
latter finds exemplification in the properly Fig. bi. 

constructed foundation of a wall containing a number of openings. 
For example, in Fig. 52, if the foundation is uniform under the 

entire front, the center of pressure must be 
outside of the center of the base ; and conse¬ 
quently the two side walls will incline outward, 
and show cracks over the openings. If the 
width of the foundation under the openings 
be decreased, or if this part of the foundation 
be omitted entirely, the center of pressure 
will fall inside of the center of base and the 
walls will tend to incline inwards, and hence 
be stable. 

299. Conclusions. One conclusion to be 
Fig. 52. drawn from the above examples is that the 

foundation of a wall should never be connected with that of another 
wall either much heavier or much lighter than itself. Both are 
equally objectionable. 

A second conclusion is that the axis of the load should strike a 
little inside of the center of the area of the base, to make sure that 
it will not be outside . Any inward inclination of the wall is ren¬ 
dered impossible by the interior walls of the building, the floor- 
beams, etc.; while an outward inclination can be counteracted only 
by anchors and the bond of the masonry. A slight deviation of the 
axis of the load outward from the center of the base has a marked 
effect, and is not easily counteracted by anchors. 

* For an account showing the violation of this principle in the construction of 
the Cooper Institute Building, New York City, and the method used to remedy it, see 
■Sanitary Engineer , vol. xii. pp. 465-68. 

































204 


ORDINARY FOUNDATIONS. 


[CHAP. X. 


The above conclusions may be summarized in the following 
principle : All foundations should be so constructed as to compress 
the ground slightly concave upwards , rather than convex up¬ 
wards. On even slightly compressible soils, a small difference in 
the pressure on the foundation will be sufficient to cause the bed to 
become convex upwards. At Chicago, an omission of 1 to 2 per 
cent, of the weight (by leaving openings) usually causes sufficient 
convexity to produce unsightly cracks. With very slight differences 
of pressure on the foundation, it is sufficient to tie the building 
together by careful bonding, by hoop-iron built in over openings, 
and by heavy bars built in where one wall joins another. 

300. Independent Piers. The art of constructing founda¬ 
tions on compressible soil has been brought to a high degree of 
development by the architects of Chicago. The special feature of 
the practice in that city is what is called “ the method of independ¬ 
ent piers;” that is, each tier of columns, each pier, each wall, etc., 
has its own independent foundation, the area of which is propor¬ 
tioned to the load on that part.* The interior walls are fastened to 
the exterior ones by anchors which slide in slots. For a detailed 
account of the methods employed in one of the best and largest 
buildings erected there, see Sanitary Engineer , Dec. 10, 1885. 

301. Effect of the Wind. Overturning. The preceding dis¬ 
cussion refers to the total weight that is to come upon the foun¬ 
dation. The pressure of the wind against towers, 
tall chimneys, etc., transfers the point of applica¬ 
tion of the load to one side of the foundation. The 
method of computing the position of the center 
of the pressure on the foundation under the action 
of the wind is illustrated in Fig. 53, in which 

ABED represents a vertical section of the. 
tower; 

a is a point horizontally opposite the center of 
the surface exposed to the pressure of the 
wind and vertically above the center of grav- 
Fig. 53. ity of the tower; 



* This method was first made known to the public by Frederick Bauman, of Chi¬ 
cago, in a pamphlet entitled “ The Method of Constructing Foundations on Isolated 
Piers,” published by him in 1872. The above examples and principles are from that 
pamphlet. 









ART. 2.] 


DESIGNING THE FOOTING. 


205 


C is the position of the center of pressure when there is no wind ; 
N is the center when the wind is acting. 

For convenience, let 

P — the maximum pressure on the foundation, per unit of area; 
p = the pressure of the wind per unit of area (see § 295); 

H = the total pressure of the wind against the exposed surface; 
W — the weight of that part of the structure above the section 
considered,—in this case, A B ; 

S = the area of the horizontal cross section; 

I = the moment of inertia of this section ; 
l = the distance A B ; 
h = the distance a C ; 
d = the distance N C ; 

M — the moment of the wind. 

When there is no horizontal force acting, the load on A B is 
uniform ; but when there is a horizontal force acting—as, for ex¬ 
ample, the wind blowing from the right,—the pressure is greatest 
near A and decreases towards B. To find the law of the variation 
of this pressure, consider the tower as a cantilever beam. The 
maximum pressure at A will be that due to the weight of the tower 
plus the compression due to flexure ; and the pressure at B will be 
the compression due to the weight minus the tension due to flexure. 

W 

The uniform pressure due to the weight is —. The strain at A due 

Ml 

to flexure is, by the principles of the resistance of materials, 


Then the maximum pressure per unit of area at A is 


P = 


W Ml 

s + 2 r 9 



and the minimum pressure at B is 



Ml 

2/ 



Equations (1) and (2) are perfectly general; they are applicable 
to any cross section, and also to any system of horizontal and ver¬ 
tical forces. In succeeding chapters they will be employed in 
finding the unit pressure in masonry dams, bridge piers, arches, 
etc. 









ORDINARY foundations. 


[chap. s. 


•206 


The value of 1 in the above formulas is given in Fig. 54 for the 
sections occurring most frequently in practice. Notice that l is the 
dimension parallel to the direction of the wind, and b the dimen¬ 
sion perpendicular to the direction of the wind. 




l = T \(b P-h IP) 

Fig. 54. 


I — gV Tt P 


I — 7t (P — Ip) 




302. If the area of the section A B, Fig. 53, is a rectangle, 
S = lb, and I = -fab l\ Substituting these values in equation (1) 


gives 


W 64/ 
~ l b'b l r 



The moment of the wind, M f is equal to the product of its total 
pressure, H, and the distance, b, of the center of pressure above 
the horizontal section considered ; or M = H . li. H is equal to 
the pressure per unit of area, p, multiplied by the area of the sur¬ 
face exposed to the pressure of the wind. Substituting the above 
value of M in equation (3) gives 


P = 


W 6 H. h 
ib + bv ' 



To still further simplify the above formula, notice that Fig. 53 
gives the proportion 

II: W :: NC :aC 9 

from which 

II. a C = W.NC \; 
or, changing the nomenclature, 

II h = Wd. 


Notice that the last relation can also be obtained directly by the 
principle of moments. Substituting the value of H . h 9 as above, in 
equation (4) gives 


P = 


W 6 W d 
Tb + ~bl~’ 



which is a convenient form for practical application. 
















AET. 2.] 


DESIGNING THE FOOTING. 


20? 


An examination of equation (5) shows that when d = N C — \ 
the maximum pressure at A is twice the average. Notice also that 
under these conditions the pressure at B is zero. This is equiva¬ 
lent to what is known, in the theory of arches, as the principle of 
the middle third. It shows that as long as the center of pressure 
lies in the middle third, the maximum pressure is not more than 
twice the average pressure, and that there is no tension at B. 

The above discussion of the distribution of the pressure on the 
foundation is amply sufficient for the case in hand ; however, the 
subject is discussed more fully in the chapter on Stability of Masonry 
Dams (see Chapter NIII). 

3G3. The average pressure per unit on A B has already been 
adjusted to the safe bearing power of the soil, and if the maximum 
pressure at A does not exceed the ultimate bearing power, the occa¬ 
sional maximum pressure due to the wind will do no harm ; but if 
this maximum exceeds or is dangerously near the ultimate strength 
of the soil, the base must be widened. 

304. Sliding. The pressure of the wind is a force tending to 
slide the foundation horizontally. This is resisted by the friction 
caused by the weight of the entire structure, and also by the earth 
around the base of the foundation, and hence there is no need, in 
this connection, of considering this manner of failure. 

305. Designing the Footing. The term footing is usually un¬ 
derstood as meaning the bottom course or courses of masonry which 
extend beyond the faces of the wall. It will be used here as apply¬ 
ing to the material—whether masonry, timber, or iron—employed 
to increase the area of the base of the foundation. _ Whatever the 
character of the soil, footings should extend beyond the face of the 
wall (1) to add to the stability of the structure and lessen the dan¬ 
ger of the work’s being thrown out of plumb, and (2) to distribute 
the weight of the structure over a larger area and thus decrease 
the settlement due to the compression of the ground. To serve 
the first purpose, footings must be securely bonded to the body of 
the wall; and to produce the second effect, they must have sufficient 
strength to resist the transverse strain to which they are exposed. 
In ordinary bui-ldings the distribution of the weight is more impor¬ 
tant than adding to the resistance to overturning, and hence only 
the former will be considered here. 

The area of the foundation may be increased until the inherent 



208 


ORDINARY FOUNDATIONS. 


[CHAP. X. 


bearing power of the area covered is sufficient to support the load 
(1) by extending the bottom courses of masonry, or (2) by the use 
of one or more layers of timbers, railroad rails, or steel I-beams, or 
(3) by resting the structure upon inverted masonry arches. 

306. Off-sets of Masonry Footings. The area of the foundation 
having been determined and its center having been located with 
reference to the axis of the load (§ 297), the next step is to deter¬ 
mine how much narrower each footing course may be than the one 
next below it. The projecting part of the footing resists as a beam 
fixed at one end and loaded uniformly. The load is the pressure 
on the earth or on the course next below. The off-set of such a 
course depends upon the amount of the pressure, the transverse 
strength of the material, and the thickness of the course. 

To deduce a formula for the relation between these quantities, 
let 

P — the pressure, in tons per square foot, at the bottom of the 
footing course under consideration ; 

R =■ the modulus of rupture of the material, in pounds per 
square inch ; 

p = the greatest possible projection of the footing course, in 
inches ; 

t = the thickness of the footing course, in inches. 

The part of the footing course that projects beyond the one above 
it, is a cantilever beam uniformly loaded. From the principles of 
the resistance of materials, we know that the upward pressure of the 
earth against the part that projects multiplied by one half of the 
length of the projection is equal to the continued product of one 
sixth of the modulus of rupture of the material, the breadth of the 
footing course, and the square of the thickness. Expressing this 
relation in the above nomenclature and reducing, we get the for¬ 
mula 

p = TP.(«) 

or, with sufficient accuracy, 

P = it .(7) 

Hence the projection available with any given thickness, or the 
thickness required for any given projection, may easily be computed 








ART. 2 .] 


DESIGNING THE FOOTING. 


209 


by equation (7). Notice that with the off-set given by the above 
formula the stone would be on the point of breaking. 

307. The margin to be allowed for safety will depend upon the 
care used in computing the loads, in selecting the materials for the 
footing courses, and in bedding and placing them. If all the loads 
have been allowed for at their probable maximum value, and if the 
material is to be reasonably uniform in quality and laid with care, 
then a comparatively small margin for safety is sufficient; but if 
all the loads have not been carefully computed, and if the job is to 
be done by an unknown contractor, and neither the material nor 
the work is to be carefully inspected, then a large margin is neces¬ 
sary. As a general rule, it is better to assume, for each particular 
case, a factor of safety in accordance with the attendant conditions 
of the problem than blindly to use the results deduced by the 
application of some arbitrarily assumed factor. The following table 
is given for the convenience of those who may wish to use 10 as a 
factor of safety. 

TABLE 25. 


Safe Off-set for Masonry Footing Courses, in Terms of the Thick¬ 
ness of the Course, using 10 as a Factor of Safety. 

For limitations, see § 308. 


Kind of Stone. 


Blue-stone flagging (see page 13) 

Granite (see page 13). 

Limestone (see page 13). 

Sandstone (see page 13). 

Slate (see page i3). 


Best Ha> d Brick (see pages 40, 41)... 

Hard Brick (see pages 40, 41). 

l 1 Portland 

Concrete (see page 112^) - 2 sand 

(3 pebbles 
( 1 Portland 

Concrete (see page 112a) - 3 sand 

(5 pebbles 


! 4 weeks 
old 

( 4 weeks 
j old 


R , IN LBS. 
PERSQ. IN. 

Off-set for a Pres¬ 
sure, IN TONS PER SQ. 
ft., on the Bottom of 
the Course, of 

0.5 

1.0 

2.0 

—+ 

2,700 

3.6 

2.6 

1.8 

1,800 

2.9 

2.1 

1.5 

1,500 

2.7 

1.9 

1.3 

1,200 

2.6 

1.8 

1.3 

5,400 

5.0 

3.6 

2.5 

1,500 

2.7 

1.9 

1.3 

800 

1.9 

1.4 

0.8 

150 

0.8 

0.6 

0.4 

80 

0.6 

0.4 

0.3 


To illustrate the method of using the preceding table, assume 
that it is desired to determine the off-set for a limestone footing 
course when the pressure on the bed of the foundation is 1 ton per 
square foot, using 10 as a factor of safety. In the table, opposite 
























210 


ORDINARY FOUNDATIONS. 


[CHAP. X* 


limestone, in next to the last column, we find the quantity 1.9* 
This shows that, under the conditions stated, the off-set may be 1.9 
times the thickness of the course. 

The values in the table agree very well with the practice of the 
principal architects and engineers for hammer-dressed stones laid 
in good cement mortar. 

If it is desired to use any other factor of safety, it is only neces¬ 
sary to substitute for R, in the preceding formula, the desired frac¬ 
tional part of that quantity as given in the second column of the 
above table. For example, assume that it is necessary to use lime¬ 
stone in the foundation, and that it is required to draw in the foot¬ 
ing courses as rapidly as possible. Assume also that the pressure, 
P, on the base of the foundation is 2 tons per square foot. If the 
limestone is of the best, and if it is laid with great care, it will be 
sufficient to use 4 as a factor of safety. Under these conditions, 
equation (7) as above gives 




X 1500 

O 


2.3 t. 


That is, the projection may be 2.3 times the thickness of the course. 

308 . Strictly, the above computations are correct only for the 
lower off-set, and then only when the footing is composed of stones 
whose thickness is equal to the thickness of the course and which 
project less than half their length, and which are also well bedded. 
The resistance of two or more courses to bending varies as the square 
of their depth, and the bending due to the uniform pressure on the 
base will also increase as the square of the sum of the projections, 
and therefore the successive off-sets should be proportional to the 
thickness of the course; or, in other words, the values as above are 
applicable to any course, provided no stone projects more than half 
its length beyond the top course. 

The preceding results will be applicable to built footing courses 
only when the pressure above the course is less than the safe strength 
of the mortar (see § 133 and g 157 a). The proper projection for 
rubble masonry lies somewhere between the values given for stone 
and those given for concrete. If the rubble consists of large stones 
well bedded in good strong mortar, then the values for this class of 
masonry will be but little less than those given in the table. If the 
rubble consists of small irregular stones laid with Portland or nat- 







ART. 2 .] 


DESIGNING THE FOOTING. 


211 


iiral cement inortar, the projection should not much exceed that 
given for concrete. If the rubble is laid in lime mortar, the pro¬ 
jection of the footing course should not be more than half that 
allowed when cement mortar is used. 

309 . Timber Footing. In very soft earth it would be inexpe¬ 
dient to use masonry footings, since the foundation would be very 
deep or occupy the space usually devoted to the cellar. One method 
of overcoming this difficulty consists in constructing a timber grat¬ 
ing, sometimes called a grillage, by setting a series of heavy timbers 
firmly into the soil, and laying another series transversely on top of 
these. The timbers may be fastened at their intersections by spikes 
or drift-bolts (§ 381) if there is any possibility of sliding, which is 
unlikely in the class of foundations here considered. The earth 
should be packed in between and around the several beams. A 
flooring of thick planks, often termed a 'platform, is laid on top of 
the grillage to receive the lowest course of masonry. In extreme 
cases, the timbers in one or more of the courses are laid close to¬ 
gether. Timber should never be used except where it will be always 
wet. 

The amount that a course of timber may project beyond the one 
next above it can be determined by equation (7), page 208. Making 
R in that equation equal to 1,000—the value ordinarily used,—and 
solving, we obtain the following results for the safe projection: If 
the pressure on the foundation is 0.5 ton per square foot, the safe 
projection is 7.5 times the thickness of the course ; if the pressure 
is 1 ton per square foot, the safe projection is 5.3 times the thick¬ 
ness of the course ; and if the pressure is 2 tons per square foot, the 
safe projection is 3.7 times the thickness of the course. The above 
values give a factor of safety of about 10. To use any other factor, 
insert in equation (7), above, the corresponding fractional part of the 
ultimate transverse strength of the particular timber to be used, 
and solve. 

The above method of computation is not applicable to two or 
more courses of timber, if one is transverse to the other. 

310 . This method of increasing the area of the footing is much 
used at New Orleans. The Custom-house at that place is founded 
upon a 3-inch plank flooring laid 7 feet below the street pavement. 
A grillage, consisting of timbers 12 inches square laid side by side, 
is laid upon the floor, over which similar timbers are placed trans¬ 
versely, 2 feet apart in the clear. 




212 


ORDINARY FOUNDATIONS. 


[CHAP. X. 


Most of the buildings of the World’s Columbian Exposition, 
Chicago, 1893, were founded upon timber footings. 

311. Steel Footing. Very recently, steel, usually in the form 
of railroad rails or I-beams, has been used instead of timber in 
foundations. The rails or I-beams are placed side by side, and 
concrete is rammed in between them. 

Steel is superior to timber for this purpose, in that the latter 
can be used only where it is always wet, while the former is not 
affected by variations of wetness and dryness. Twenty years’ ex¬ 
perience in this use of steel at Chicago shows that after a short time 
the surface of the metal becomes encased in a coating which pre¬ 
vents further oxidation. The most important advantage, however, 
in this use of steel is that the off-set can be much greater with steel 
than with wood or stone; and hence the foundations may be shal¬ 
low, and still not occupy the cellar space. 

The proper projections for the steel beams can be computed by 
a formula somewhat similar to that of § 306; but the steel footing 
is appropriately a part of the steel-skeleton construction, and hence 
will not be considered here. For a presentation of the method 
of computations formerly employed in Chicago, see Engineering 
JS'ews , vol. xxvi. page 122; and for adverse criticisms thereon, see 
ibid ., pages 265, 312, 415, and vol. xxxii. page 387. Concerning 
the effect of the strength of the base of the column, see Johnson’s 
“Modern Framed Structures,” pages 444-46. For a discussion 
which considers the deflection of the several beams, see Engineering 
Record , vol. xxxix. pages 333-34, 354-56, 383, 407-8. The last 
is the most exact method of analysis, and also secures the greatest 
economy of material. 

312. Inverted Arch. Inverted arches are frequently built under 
:and between the bases of piers, as shown in Fig. 55. Employed in 

this way, the arch simply distributes 
the pressure over a greater area; but 
it is not well adapted to this use, for 
(1) it is nearly impossible to prevent 
end piers of a series from being 
pushed outward by the thrust of the 
arch, and (2) it is generally impos¬ 
sible, with inverted arches, to make the areas of the different parts 
of the foundation proportional to the load to be supported (see § 



Fig. 55. 















ART. 3 .] 


PREPARING THE BED. 


213 


■297). The only advantage the inverted arch has over masonry 
footings is in the shallower foundation obtained. 

313. In a few cases masonry piers have been sunk to a solid sub¬ 
stratum by excavating the material from the inside, and then resting 
arches on these piers. This is an expensive method, and has essen¬ 
tially the same objections as the inverted arch. 

Art. 3. Preparing the Bed. 

314. On Rock. • To prepare a rock bed to receive a foundation 
it is generally only necessary to cut away the loose and decayed por¬ 
tions of the rock, and to dress it to a plane surface as nearly perpen¬ 
dicular to the direction of the pressure as is practicable. If there 
are any fissures, they should be filled with concrete. A rock that 
is very much broken can be made amply secure for a foundation by 
the liberal use of good cement concrete. The piers of the Niagara 
Cantilever Bridge are founded upon the top of a bank of bowlders, 
which were first cemented together with concrete. 

Sometimes it is necessary that certain parts of a structure 
start from a lower level than the others. In this case care should 
be taken (1) to keep the mortar-joints as thin as possible, (2) to lay 
the lower portions in cement, and (3) to proceed slowly with the 
work ; otherwise the greater quantity of mortar in the wall on the 
lower portions of the slope will cause greater settling there and a 
consequent breaking of the joints at the stepping-places. The 
bonding over the off-sets should receive particular attention. 

315. On Firm Earth. For foundations in such earths as hard 
clay, clean dry gravel, or clean sharp sand, it is only necessary to 
dig a trench from 3 to 6 feet deep, so that the foundation may be 
below the disintegrating effect of frost. Provision should also be 
made for the drainage of the bed of the foundation. 

With this class of foundations it often happens that one part of 
the structure starts from a lower level than another. When this is 
the case great care is required. All the precautions mentioned in 
the second paragraph of § 314 should be observed, and great care 
should also be taken so to proportion the load per unit of area that 
the settlement of the foundation may be uniform. This is difficult 
to do, since a variation of a few feet in depth often makes a great 
difference in the supporting power of the soil. 




214 


ORDINARY FOUNDATIONS. 


[CHAP. X. 


316. In Wet Ground. The difficulty in soils of this class is in 
disposing of the water, or in preventing the semi-liquid soil from 
running into the excavation. The difficulties are similar to those- 
met with in constructing foundations under water—see Chapter XII. 
Three general methods of laying a foundation in this kind of soil 
will be briefly described. 

317. Coffer-Dam. If the soil is only moderately wet—not satu¬ 
rated,—it is sufficient to inclose the area to be excavated with sheet 
piles (boards driven vertically into the ground in contact with each 
other). This curbing is a simple form of a coffer-dam (Art. 1, 
Chap. XII). The boards should be sharpened wholly from one- 
side ; this point being placed next to the last pile driven causes 
them to crowd together and make tighter joints. The sheeting may 
be driven by hand, by a heavy weight raised by a tackle and then 
dropped, or by an ordinary pile-driver (§§ 335-3G). Unless the- 
amount of water is quite small, it will be necessary to drive a double 
row of sheeting, breaking joints. It will not be possible to entirely 
prevent leaking. The water that leaks in may be bailed out, or 
pumped—either by hand or by steam (see § 395). 

To prevent the sheeting from being forced inward, it may be 
braced by shores placed horizontally from side to side and abutting 
against wales (horizontal timbers which rest against tlie sheet piles). 
The bracing is put in successively from the top as the excavation 
proceeds; and as the masonry is built up, short braces between the 
sheeting and the masonry are substituted for the long braces which 
previously extended from side to side. Iron screws, somewhat 
similar to jack-screws, are used, instead of timber shores, in exca¬ 
vating trenches for the foundations of buildings, for sewers, etc. 

If one length of sheeting will not reach deep enough, an addi¬ 
tional section can be placed inside of the one already in position, 
when the excavation has reached a sufficient depth to require it. 
Ordinary planks 8 to 12 inches wide and 1£ or 2 inches thick are 
used. 

For a more extended account of the use of coffer-dams, see 
Chapter XII—Foundations Under Water, Art. 1—Coffer-Dams. 

318. In some cases the soil is more easily excavated if it is first 
drained. To do this, dig a hole—a sump—into which the water will 
drain and from which it may be pumped. If necessary, several 
sumps may be sunk, and deepened as the excavation proceeds. 



ART. 3 .] 


PREPARING 'I HE RED. 


215 


Quicksand or soft alluvium may sometimes be pumped out along 
with the water by a centrifugal or a mud pump (§ 395 and § 448). 
On large jobs, such material is sometimes taken out with a clam¬ 
shell or Milroy dredge (§ 412). 

319. Concrete. Concrete can frequently be used advantage¬ 
ously in foundations in wet soils. If the water can be removed, the 
concrete should be deposited in continuous layers, about 6 inches 
thick, and gently rammed until the water begins to ooze out on the 
upper surface (see § 153). If the water can not be removed, the 
concrete may be deposited under the water (see § 154), although it 
is more difficult to insure good results by this method than when 
the concrete is deposited in the open air.* 

320. Grillage. If the semi-liquid soil extends to a considerable 
depth, or if the soft soil which overlies a solid substratum can not be 
removed readily, it is customary to drive piles at uniform distances 
over the area, and construct a grillage (see § 380) on top of them. 
This construction is very common for bridge abutments (Chapter 
XV). The piles should be sawed off (§ 378) below low-water, which 
usually necessitates a coffer-dam (§ 317, and Art. 1 of Chapter XII), 
and the excavation of the soil a little below the low-water line. 

For a more extended account of this method of laying a founda¬ 
tion, see §§ 380-82. 

321. In excavating shallow pits in sand containing a small 
amount of water, dynamite cartridges have been successfully used to 
drive the water out. A hole is bored with an ordinary auger and 
the cartridge inserted and exploded. The explosion drives the water 
back into the soil so far that, by working rapidly, the hole can be 
excavated and a layer of concrete placed before the water returns. 

322. CONCLUSION. It is hardly worth while here to discuss this 
subject further. It is one on which general instruction can not be 
given. Each case must be dealt with according to the attendant 
circumstances, and a knowledge of the method best adapted to any 
given conditions comes only by experience. 


* For the composition, cost, etc., of concrete, see Art. 2 of Chap. IV. pp. 102-12. 






CHAPTER XL 


PILE FOUNDATIONS. 

323. Definitions. Pile. Although a pile is generally under- 
stood to be a round timber driven into the soil to support a load, 
the term has a variety of applications which it will be well to explain. 

Beai'ing Pile. One used to sustain a vertical load. This is the 
ordinary pile, and usually is the one referred to when the word pile 
is employed without qualification. 

Sheet Piles. Thick boards or timbers driven in close contact 
to inclose a space, to prevent leakage, etc. Generally they are con¬ 
siderably wider than thick; but are sometimes square, in which case 
they are often called close piles. 

False Pile. A timber added to a pile after driving, to supple* 
ment its length. 

Foundation Pile. One driven to increase the supporting power 
of the soil under a foundation. 

Screw Pile. An iron shaft to the bottom of which is attached 
a broad-bladed screw having only one or two turns. 

Disk Pile. A bearing pile near the foot of which a disk is keyed 
or bolted to give additional bearing power. 

Pneumatic Pile. A metal cylinder which is sunk by atmos¬ 
pheric pressure. This form of pile will be discussed in the next 
chapter (see § 431). 

Art. 1. Descriptions, and Methods of Driving. 

324. Iron Piles. Both cast and wrought iron are employed for 
ordinary bearing piles, sheet piles, and for cylinders. Iron cylin¬ 
ders are generally sunk either by dredging the soil from the inside 
(§ 415), or by the pneumatic process (see the next chapter, particu¬ 
larly §§ 431-35). For another method of employing iron cylinders, 
see §§ 384-85. 




ART. 1.] DESCRIPTIONS, AND METHODS OF DRIVING. 


217 


Cast-iron piles are beginning to be used as substitutes for com¬ 
mon wooden ones. Lugs or flanges are usually cast on the sides of 
the piles, to which bracing may be attached for securing them in 
position. A wood block is laid upon the top of the pile to receive- 
the hammer used in driving it; and, after being driven, a cap with 
a socket in its lower side is placed upon the pile to receive the load.. 
The supporting power is sometimes increased by keying on an iron 
disk. The advantages claimed for cast-iron piles are: (1) they are 
not subject to decay; (2) they are more readily driven than wooden 
ones, especially in stony ground or stiff clay; and (3) they possess 
greater crushing strength, which, however, is an advantage only 
when the pile acts as a column (see § 355). The principal disadvan¬ 
tage is that they are deficient in transverse resistance to a suddenly 
applied force. This objection applies only to the handling of the 
piles before being driven, and to such as are liable, after being driven, 
to sudden lateral blows, as from floating ice, logs, etc. 

Recently, rolled sections of wrought-iron have been employed to a 
limited degree for bearing-piles, but present prices prohibit an ex¬ 
tended use of wrought-iron piles. It is possible that iron may take 
the place of wood for piles where they are alternately wet and dry, 
or where they are difficult to drive; but where the piles are always 
wet—as is usually the case in foundation work,—wood is as durable 
as iron; and hence, on account of cheapness, is likely to have the 
preference. 

325. SCREW Piles. These are generally wholly of iron, although 
the stem is sometimes wood. The screw pile usually consists of a 
rolled-iron shaft, 3 to 8 inches in diameter, having at its foot one or 
two turns of a cast-iron screw, the blades of which may vary from 1^ 
to 5 feet in diameter. The piles ordinarily employed for light¬ 
houses exposed to moderate seas or to heavy fields of ice have a 
shaft 3 to 5 inches in diameter and blades 3 to 4 feet in diameter, 
the screw weighing from 600 to 700 pounds. For bridge piers, 
the shafts are from 6 to 8 inches and the blades from 4 to 6 feet in 
diameter, the screw weighing from 1,500 to 4,000 pounds. 

Screw piles were invented by Mitchell of Belfast, and are largely 
used in Europe, but not to any great extent in this country. They 
have been used in founding small light-houses on the sea-shore, for 
signal stations in marine surveying, for anchorage for buoys, and 
for various purposes inland. 




218 


PILE EOTODATIOKS. 


[CHAP. XI. 


For founding beacons, etc., the screw pile has the special advan¬ 
tage of not being drawn out by the upward force of the waves against 
the superstructure. Even when all cohesion of the ground is de¬ 
stroyed in screwing down a pile, a conical mass, with its apex at the 
bottom of the pile and its base at the surface, would have to be 
lifted to draw the pile out. The supporting power also is consider- 
a! 1 owing to the increased bearing surface of the screw blade. 
Screw piles have, therefore, an advantage in soft soil. They could 
also be used advantageously in situations where the jar of driving 
ordinary piles might disturb the equilibrium of adjacent structures. 

326. These piles are usually screwed into the soil by men work¬ 
ing with capstan bars. Sometimes a rope is wound around the 
shaft and the two ends pulled in opposite directions by two capstans, 
and sometimes the screw is turned by attaching a large cog-wheel to 
the shaft by a friction-clutch, which is rotated by a worm-screw 
operated by a hand crank. Of course steam or horse-power could 
be used for this purpose. 

The screw will penetrate most soil •. It will pass through loose 
pebbles and stones without much difficulty, and push aside bowlders 
of moderate size. Ordinary clay does not present much obstruction; 
clean, dry sand gives the most difficulty. The danger of twisting 
off the shaft limits the depth to which they may be sunk. Screw 
piles with blades 4 feet in diameter have been screwed 40 feet into 
a mixture of clay and sand. The resistance to sinking increases 
very rapidly with the diameter of the screw; but under favorable 
circumstances an ordinary screw pile can be sunk very quickly. 
Screws 4 feet in diameter have, in less than two hours, been sunk 
by hand-labor 20 feet in sand and clay, the surface of which was 
20 feet below the water. For depths of 15 to 20 feet, an average of 
4 to 8 feet per day is good work for wholly hand-labor. 

For an illustrated and detailed account of the founding of a rail¬ 
road bridge pier on screw piles, see Engineering Nexus, Vol. XIII. 

pp. 210-12. 

327. Disk Piles. These differ but little from screw piles, a 
flat disk, instead of a screw, being keyed on at the foot of the iron 
stem. Disk piles are sunk by the water-jet (§ 343). One of the few 
cases in which they have been used in this country was in founding 
an ocean pier on Coney Island, near New York City. The shafts 
were wrouglit-iron, lap-welded tubes, 8f inches outside diameter, in 



ART. 1.] DESCRIPTIONS, AND METHODS OF DRIVING. 


219 


sections 12 to 20 feet long ; the disks were 2 feet in diameter and 
9 inches thick, and were fastened to the shaft by set-screws. Many 
of the piles were 57 feet long, of which 17 feet was in the sand.* 

328. Sand Piles. For an account of the method of using sand 
as piles, see § 288. 

329. Sheet Piles. These are flat piles, which, being driven 
successively edge to edge, form a vertical or nearly vertical sheet 
for the purpose of preventing the materials of a foundation from 
spreading, or of guarding them against the undermining action of 
water. They may be made either of timber or iron. Ordinarily 
sheet piles are simply thick planks, sharpened and driven edge to 
edge. Sometimes they have a tongue on one edge and a correspond¬ 
ing groove on the other, to aid in guiding them into place while 
driving. When heavy timbers are employed as sheet piling, wooden 
blocks or iron lugs are fastened on the edges to assist in guiding 
them into position. Sheet piles should be sharpened wholly, or at 
least mainly, from one side, and the long edge placed next to the 
pile already driven. This causes them to crowd together and 
make comparatively close joints. 

When a space is to be inclosed with sheet piling, two rows of 
guide piles are first driven at regular intervals of from 6 to 10 feet, 
and to opposite sides of these, near the top, are notched or bolted a 
pair of parallel string-pieces, or wales , from 5 to 10 inches square, 
so fastened to the guide piles as to leave a space between the wales 
equal to the thickness of the sheet piles. If the sheeting is to stand 
more than 8 or 10 feet above the ground, a second pair of wales is 
required near the level of the ground. The sheet piles are driven 
(§§ 334-45) between the wales, working from both ends towards 
the middle of the space between a pair of guide piles, so that the 
last or central pile acts as a wedge to tighten the whole. 

330. Wooden Bearing Piles. Spruce and hemlock answer 
very well, in soft or medium soils, for foundation piles or for piles 
always under water ; the hard pines, elm, and beech, for firmer 
soils ; and the hard oaks, for still more compact soils. Where the 
pile is alternately wet and dry, white or post oak and yellow or 
southern pine are generally used. 


* For a detailed and illustrated description of this work, see an article by Charles 
Macdonald, C.E., in Trans. Am. Soc. of C. E., Vol. VIII. pp. 227-37. 





220 


PILE FOUNDATIONS. 


[CHAP, xr 


Piles should never be less than 8 inches in diameter at the small 
end and never more than 18 inches at the large end. Specifications 
usually require that these dimensions shall not be less than 10 nor 
more than 14 inches respectively. Piles should be straight-grained, 
should be trimmed close, and should have the bark removed. 

331. Specifications for Piles. The ordinary specifications are 
about as follows :* 

Piles, whether used in foundations, trestle-work, or pile bridges, shall be 
of good quality, sound, white oak’or such other timber as the engineer may 
direct, not less than ten inches (10") in diameter at the smaller end and 
14 inches (14") at the larger, and of such lengths as the engineer may require. 
They must be straight-grained, must be trimmed close, and must have all the 
bark taken off before being driven. They must be cut off square at the butt, 
and be properly sharpened. If required by the engineer, the point shall be 
shod with iron shoes [see § 332], and the head hooped w r itk iron bands of ap¬ 
proved size and form [see § 332], which will be paid for by the pound. 

332. Pile Caps and Shoes. To prevent bruising and splitting 
in driving, 2 or 3 inches of the head is usually chamfered off. As 
an additional means of preventing splitting, the head is often 
hooped with a strong iron band, 2 to 3 inches wide and to 1 inch 
thick. The expense of removing these bands and of replacing the 
broken ones, and the consequent delays, led to the introduction 
recently, of a cap for the protection of the head of the pile. The 
cap consists of a cast-iron block with a tapered recess above and 
below, the chamfered head of the pile fitting into the lower recess 
and a cushion piece of hard wood, upon which the hammer falls, 
fitting into the upper one. The cap preserves the head of the pile, 
adds to the effectiveness of the blows (§ 361), and keeps the pile head 
in place to receive the blows of the hammer. 

A further advantage of the pile cap is that it saves piles. In 
hard driving, without the cap the head is crushed or broomed to 
such an extent that the pile is adzed or sawed off several times 
before it is completely driven, and often after it is driven a portion 
of the head must be sawed off to secure sound wood upon which to 
rest the grillage or platform (§ 380). In ordering piles for any 
special work where the driving is hard, allowance must be made for 
this loss. 

Piles are generally sharpened before being driven, and some- 

* See also “ Piling” in the general specifications for railway masonry, as given in 
Appendix I. 





ART. 1.] DESCRIPTIONS, AND METHODS OF DRIVING. 


221 


times, particularly in stony ground, the point is protected by an 
iron shoe. The shoe may be only two V -shaped loops of bar iron 
placed over the point, in planes at right angles to each other, and 
spiked to the piles ; or it may be a wrought or cast iron socket, of 
which there are a number of forms on the market. 

333. Splicing Piles. It frequently happens, in driving piles in 
swampy places, for false-works, etc., that a single pile is not long 
enough, in which case two are spliced together. A common method 
of doing this is as follows :* after the first pile is driven its head is 
cut off square, a hole 2 inches in diameter and 12 inches deep is 
bored in its head, and an oak treenail, or dowel-pin, 23 inches 
long, is driven into the hole ; another pile, similarly squared and 
bored, is placed upon the lower pile, and the driving continued. 
Spliced in this way the pile is deficient in lateral stiffness, and tho 
upper section is liable to bounce off while driving. It is better to 
reinforce the splice by flatting the sides of the piles and nailing on, 
with say 8-inch spikes, four or more pieces 2 or 3 inches thick, 4 or 
5 inches wide, and 4 to 6 feet long. In the erection of the bridge 
over the Hudson at Poughkeepsie, N. Y., two piles were thus 
spliced together to form a single one 130 feet long. 

Piles may be made of any required length or cross-section by 
bolting and fishing together, sidewise and lengthwise, a number of 
squared timbers. Such piles are frequently used as guide piles in 
sinking pneumatic caissons (§ 436). Hollow-built piles, 40 inches 
in diameter and 80 feet long, were used for this purpose in con¬ 
structing the St. Louis Bridge (§ 457). They were sunk by pump¬ 
ing the sand and water from the inside of them with a sand pump 
(§ 448). 

334. Pile-driving Machines. Pile-driving machines may be 
classified according to the character of the driving power, which 
may be (1) a falling weight, (2) the force of an explosive, or (3) the 
erosive action of a jet of water. Piles are sometimes set in holes 
bored with a well-auger, and the earth rammed around them. This 
is quite common in the construction of small highway bridges in 
the prairie States, a 10- or a 12-inch auger being generally used. 
The various pile-driving machines will now be briefly described and 
compared. 

* See “ Piling” in the General Specifications for Railroad Masonry, as given in 
Appendix 1. 






222 


PILE FOUNDATIONS. 


[CHAP. XI. 


335. Drop-hammer Pile-driver. The usual method of driving 
piles is by a succession of blows given w r ith a heavy block of wood 
or iron—called a ram, monkey, or hammer—which is carried by a 
rope or chain passing over a pulley fixed at the top of an upright 
frame, and allowed to fall freely on the head of the pile. The 
machine for doing this is called a drop-hammer pile-driver, or a 
monkey pile-driver—usually the former. The machine is generally 
placed upon a car or scow. 

The frame consists of two uprights, called leaders, from 10 to 00 
feet long, placed about 2 feet apart, which guide the falling weight 
in its descent. The leaders are either wooden beams or iron chan¬ 
nel-beams, usually the former. The hammer is generally a mass of 
iron weighing from 500 to 4,000 pounds (usually about 2,000) with 
grooves in its sides to fit the guides and a staple in the top by which 
it is raised. The rope employed in raising the hammer is usually 
wound up by a steam-engine placed on the end of the scow or car, 
opposite the leaders. 

A car pile-driver is made especially for railroad work, the 
leaders resting upon an auxiliary frame, by which piles may be 
driven 14 to 16 feet in advance of the end of the track ; and the 
frame is pivoted so that piles may be driven on either side of the 
track. This method of pivoting the frame carrying the leaders is 
also sometimes applied to a machine used in driving piles for foun¬ 
dations. 

In railroad construction, it is not possible to use the pile-driving 
car with its steam-engine in advance of the track ; hence, in this 
kind of work, the leaders are often set on blocking and the ham¬ 
mer is raised by horses hitched directly to the end of the rope. 
Portable engines also are sometimes used for this purpose. Occa¬ 
sionally the weight is raised by men with a windlass, or by pulling 
directly on the rope. 

A machine used for driving sheet piles differs from that de¬ 
scribed above in one particular, viz.: it has but one leader, in front 
of which the hammer moves up and down. With this construction, 
the machine can be brought close up to the wall of a coffer-dam 
(§ 317 and § 390), and the pile already driven does not interfere 
with the driving of the next one. 

336. There are two methods of detaching the weight, i . e ., of 
letting the hammer fall: (1) by a nipper, and (2) by a friction-clutch. 




ART. 1.] DESCRIPTIONS, AND METHODS OE DRIVING. 


223 


1. The nipper consists of a block which slides freely between 
the leaders and which carries a pair of hooks, or tongs, projecting 
from its lower side. The tongs are so arranged that when lowered 
on to the top of the hammer they automatically catch in the staple 
in the top of the hammer, and hold it while it is being lifted, until 
they are disengaged by the upper ends of the arms striking a pair of 
inclined surfaces in another block, the trip , which may be placed 
between the leaders at any elevation, according to the height of fall 
desired. 

With this form of machine, the method of operation is as fol¬ 
lows : The pile being in place, with the hammer resting on the head 
of it and the tongs being hooked into the staple in the top of the 
hammer, the rope is wound up until the upper ends of the tongs 
strike the trip, which disengages the tongs and lets the hammer 
fall. As the hoisting rope is unwound the nipper block follows the 
hammer, and, on reaching it, the tongs automatically catch in the 
staple, and the preceding operations may be repeated. This method 
is objectionable owing to the length of time required (a) for the 
nipper to descend after the hammer has been dropped, and (b) to 
move the trip when the height of fall is changed. Some manufac¬ 
turers of pile-driving machinery remove the last objection by making 
an adjustable trip which is raised and lowered by a light line pass¬ 
ing over the top of the leaders. This is a valuable improvement. 

When the rope is wound up by steam, the maximum speed is 
from 6 to 14 blows per minute, depending upon the distance the 
hammer falls. The speed can not be increased by the skill of the 
operator, although it could be by making the nipper block heavier. 

2. The method by using a f riction-clutch, or friction-drum, as it 
is often called, consists in attaching the rope permanently to the 
staple in the top of the hammer, and dropping the hammer by set¬ 
ting free the winding drum by the use of a friction-clutch. The 
advantages of this method are (a) that the hammer can be dropped 
from any height, thus securing a light or heavy blow at pleasure; 
and ( b) that no time is lost in waiting for the nipper to descend and 
in adjusting the trip. 

When the rope is wound up by steam, the speed is from 20 to 
30 blows per minute, but is largely dependent upon the skill of the 
man who controls the friction-clutch. The hammer is caught on 
the rebound, is elevated with the speed of a falling body, and hence 





224 


PILE FOUNDATIONS. 


[CHAP. XI. 

the absolute maximum speed is attained. The rope, by which the 
hammer is elevated, retards the falling weight; and hence, for an 
equal effect, this form requires a heavier hammer than when the 
nipper is used. Although the friction-drum pile-driver is much 
more efficient, it is not as generally used as the nipper driver. The 
former is a little more expensive in first cost. 

337. Steam-hammer Pile-driver. As regards frequency of use, 
the next machine is probably the steam-hammer pile-driver, invented 
by Nasmyth* in 1839. It consists essentially of a steam cylinder 
(stroke about 3 feet), the piston-rod of which carries a weight of 
about 3,500 pounds. The steam-cylinder is fastened to and between 

the tops of two I-beams about 8 to 10 feet 
long, the beams being united at the bottom by 
a piece of iron in the shape of a frustum of a 
cone, which has a hole through it. The under 
side of this connecting piece is cut out so as to 
fit the top of the pile. The striking weight, which 
works up and down between the two I-beams 
as guides, has a cylindrical projection on the 
bottom which passes through the hole in the 
piece connecting the feet of the guides and 
strikes the pile. The steam to operate the ham¬ 
mer is conveyed from the boiler through a flex¬ 
ible tube. Fig. 56 shows the striking weight of 
the latest form of steam-hammer. It differs 
from that described above in having four rods 
for guides, instead of the two I-beams. 

The whole mechanism can be raised and 
lowered by a rope passing over a pulley in the 
top of the leaders. After a pile has been placed 
in position for driving, the machine is lowered 
upon the top of it and entirely let go, the pile 
being its only support. When steam is admitted 
below the piston, it rises, carrying the striking 
weight with it, until it strikes a trip, which 
cuts off the steam, and the hammer falls by its 
own weight. At the end of the down stroke the valves are again 

* It is ordinarily called Nasmyth’s hammer, but Bourdon should at least share 
the credit (see Engineering News, vol. xiii. pp. 59, 60). 


















































































ART. 1.] 


DESCRIPTIONS, AND METHODS OF DRIVING. 


225 


automatically reversed, and the stroke repeated. By altering the 
adjustment of this trip-piece, the length of stroke (and thus the 
force of the blows) can be increased or diminished. The admission 
and escape of steam to and from the cylinder can also be controlled 
directly by the attendant, and the number of blows per minute 
is increased or diminished by regulating the supply of steam. The 
machine can give 60 to 80 blows per minute. 

338. Drop-hammer vs. Steam-hammer. The drop-hammer is 
capable of driving the pile against the greater resistance. The 
maximum fall of the drop-hammer is 40 or 50 feet, while that of 
the steam-hammer is about 3 feet. The drop-hammer ordinarily 
weighs about 1 ton, while the striking weight of the steam-hammer 
usually weighs about 1J tons. The energy of the maximum blow 
of the drop-hammer is 45 foot-tons (= 45 ft. X 1 ton), and the 
energy of the maximum blow of the steam-hammer is 4.5 foot-tons 
(— 3 ft. X 14 tons). The energy of the maximum blow of the 
drop-hammer is, therefore, about 10 times that of the steam- 
hammer. 

However, the effectiveness of a blow does not depend alone upon 
its energy. A considerable part of the energy is invariably lost by 
the compression of the materials of the striking surfaces, and the 
greater the velocity the greater this loss. An extreme illustration 
of this would be trying to drive piles by shooting rifle-bullets at 
them. A 1-ton hammer falling 45 ft. has 10 times the energy of a 
li-ton hammer falling 3 ft., but in striking, a far larger part of the 
former than of the latter is lost by the compression of the pile head. 
In constructing the foundation of the Brooklyn dry dock, it was 
practically demonstrated that “there was little, if any, gain in 
having the fall more than 45 feet.” The Joss due to the compres¬ 
sion depends upon the material of the pile, and whether the head of 
it is bruised or not. The drop-hammer, using the pile-cap and the 
friction-drum, can drive a pile against a considerably harder resist¬ 
ance than the steam-hammer. 

It is frequently claimed that the steam-hammer can drive a pile 
against a greater resistance than the drop-hammer. As compared 
with the old style drop-hammer, i. e., without the friction-drum 
.and the pile-cap, this is probably true. The striking of the weight 
upon the head of the pile splits and brooms it very much, which 
materially diminishes the effectiveness of the blow. In hard driving 



226 


PILE FOUNDATIONS. 


[CHAP. XI. 


with the drop-hammer, without the pile-cap, the heads of the piles, 
even when hooped, will crush, bulge out, and frequently split for 
many feet below the hoop. For this reason, it is sometimes speci¬ 
fied that piles shall not be driven with a drop-hammer. 

The rapidity, of the blows is an important item as affecting the 
efficiency of a pile-driver. If the blows are delivered rapidly, 
the soil does not have sufficient time to recompact itself about 
the pile. With the steam-driver the blows are delivered in such 
quick succession that it is probable that a second blow is de¬ 
livered before the pile has recovered from the distortion produced 
by the first, which materially increases the effectiveness of the 
second blow. In this respect the steam-hammer is superior to the 
drop-hammer, and the friction-clutch driver is superior to the 
nipper driver. 

In soft soils, the steam-hammer drives piles faster than either 
form of the drop-hammer, since after being placed in position on 
the head of the pile it pounds away without the loss of any time. 

339. Ina rough way the first cost of the two drivers—exclusive 
of scow or car, hoisting engine, and boiler, which are the same in 
each—is about $80 for the drop-hammer driver, and about $800 for 
the steam-driver. Of course these prices will vary greatly. The per 
cent, for wear and tear is greater for the drop-hammer than for the 
steam-hammer. For work at a distance from a machine-shop the 
steam-driver is more liable to cause delays, owing to breakage of 
some part which can not be readily repaired. 

340. Gunpowder Pile-driver. This machine was invented by 
Shaw, of Philadelphia, in 1870. The expansive force of gunpowder 
is utilized both in driving the pile and in raising the ram. The 
essential parts of the machine are the ram and gun. The former 
consists of a mass of iron weighing generally about 1,500 pounds, 
which terminates below in a sort of piston ; this piston fits tightly 
into a chamber in another mass of iron, the gun. The ram travels 
between vertical guides much as in the other machines ; and the 
gun and ram are hoisted as is the steam-hammer. The ram having 
been raised to the top of the guides, and the gun placed upon the 
top of the pile, a cartridge of from 1 to 3 ounces of gunpowder 
is placed in the cylinder, or gun, and the ram is allowed to descend. 
The piston enters the cylinder, compresses the air, and generates 
heat enough to ignite the cartridge, when the expansive force of 







I 


ART. 1.] DESCRIPTIONS, AND METHODS OF DRIVING. 227 

the powder forces the pile down and the ram up. A cartridge is 
thrown into the gun each time as the ram ascends. The rapidity 
of the blows is limited by the skill of the operator and by the heat¬ 
ing of the gun. Thirty to forty blows, of from 5 to 10 feet each, 
can be made per minute. 

341. The only advantage of this machine is that the hammer 
does not come in contact with the head of the pile, and hence does 
not injure it. The disadvantages are (1) that it is of no assistance 
in handling the pile ; (2) that it is not economical; (3) that the 
gases soon destroy the gun ; (4) that a leakage of gas occurs as the 
gun gets hot, which renders it less efficient as the rapidity of firing 
is increased ; and (5) that the gun gets so hot as to explode the 
cartridge before the descent of the ram, which, of course, is an 
entire loss of the explosive. Its first cost is great. It is not now 
used. 

342. Driving Piles with Dynamite. It has been proposed to 
drive piles by exploding dynamite placed directly upon the top of 
the pile. It is not known that this method has been used except 
in a few instances. It would be a slow method, but might prove 
valuable where only a few piles were to be driven by saving the 
transportation of a machine ; or it might be employed in locations 
where a machine could not be operated. The higher grades of 
dynamite are most suitable for this purpose.* 

343. Driving Piles with Water Jet. Although the water jet 
is not strictly a pile-driving machine, the method of sinking piles 
by its use deserves careful attention, because it is often the cheapest 
and sometimes the only means by which piles can be sunk in mud, 
silt, or sand. 

The method is very simple. A jet of water is forced into the 
soil just below the point of the pile, thus loosening the soil and 
allowing the pile to sink, either by its own weight or with very light 
blows. The water may be conveyed to the point of the pile through 
a flexible hose held in place by staples driven into the pile ; and 
after the pile is sunk, the hose may be withdrawn for use again. 
An iron pipe may be substituted for the hose. It seems to make 
very little difference, either in the rapidity of the sinking or in the 
accuracy with which the pile preserves its position, whether the 
nozzle is exactly under the middle of the pile or not. 


* For a brief description of explosives, see pp. 119-24. 






228 


PILE FOUNDATIONS. 


[CHAP. XI. 


The water jet seems to have been first used in engineering in 
1852, at the suggestion of General Geo. B. McClellan. It has been 
'extensively employed on the sandy shores of the Gulf and South 
Atlantic States, where the compactness of the sand makes it diffi¬ 
cult to obtain suitable foundations for light-houses, wharves, etc. 
Another reason for its use in that section is, that the palmetto piles 
—the only ones that will resist the ravages of the teredo—are too 
soft to withstand the blows of the drop-hammer pile-driver. By 
'employing the water jet the necessity for the use of the pile-hammer 
is removed, and consequently palmetto piles become available. 
The jet has also been employed in a great variety of ways to facili¬ 
tate the passage of common piles, screw and disk piles, cylinders, 
^caissons, etc., etc., through earthy material.* 

344. The efficiency of the jet depends upon the increased fluidity 
given to the material into which the piles are sunk, the actual dis¬ 
placement of material being small. Hence the efficiency of the jet is 
greatest in clear sand, mud, or soft clay; in gravel, or in sand con¬ 
taining a large percentage of gravel, or in hard clay, the jet is almost 
useless. For these reasons the engine, pump, hose, and nozzle 
should be arranged to deliver large quantities of water with a mod¬ 
erate force, rather than smaller quantities with high initial velocity. 
In gravel, or in sand containing considerable gravel, some benefit 
might result from a velocity sufficient to displace the pebbles and 
drive them from the vicinity of the pile ; but it is evident that 
any practicable velocity would be powerless in gravel, except for a 
very limited depth, or where circumstances favored the prompt 
removal of the pebbles. 

The error most frequently made in the application of the water 
jet is in using pumps with insufficient capacity. Both direct-acting 
and centrifugal pumps are frequently employed. The former 
affords the greater power ; but the latter has the advantage of a less 
first cost, and of not being damaged as greatly by sand in the water 
used. 

The pumping plant used in sinking the disk-piles for the Coney 
Island pier (see § 327), “consisted of a Worthington pump with a 
12-inch steam cylinder, 8-£-inch stroke, and a water cylinder 7-J- 
inches in diameter. The suction hose was 4 inches in diameter, 

* See a pamphlet—“ The Water Jet as an Aid to Engineering Construction”_ 

published (1881) by the Engineer Department of the U. S. Army. 






ART. 1.] DESCRIPTIONS, AND METHODS OF DRIVING. 


229 


and the discharge hose, which was of four-ply gum, was 3 inches. 
The boiler was upright, 42 inches in diameter, 8 feet high, and 
contained G2 tubes 2 inches in diameter. An abundance of steam 
was supplied by the boiler, after the exhaust had been turned into 
the smoke-stack and soft coal used as fuel. An average of about 
160 pounds of coal was consumed in sinking each pile. With the 
power above described, it was found that piles could be driven in 
-clear sand at the rate of 3 feet per minute to a depth of 12 feet; 
after which the rate of progress gradually diminished, until at 18 
feet a limit was reached beyond which it was not practicable to 
go without considerable loss of time. It frequently happened that 
the pile would ‘ bring up ’ on some tenacious material which was 
assumed to be clay, and through which the water jet, unaided, 
could not be made to force a passage. In such cases it was found 
that by raising the pile about 6 inches and allowing it to drop sud¬ 
denly, with the jet still in operation, and repeating as rapidly as 
possible, the obstruction was finally overcome ; although in some in¬ 
stances five or six hours were consumed iu sinking as many feet.” * 
In the shore-protection work on the Great Lakes, under the 
direction of the United States Army engineers, the pumping plant 
“ consisted of a vertical tubular boiler, with an attached engine 
having an 8 X 12-inch cylinder, and giving about 130 revolutions per 
minute to a 42-inch driving-wheel. A No. 4 Holly rotary pump, 
with 18-inch pulley, was attached by a belt to the driving-wheel of 
the engine, giving tfbout 300 revolutions per minute to the pump. 
The pump was supplied with a 4-inch suction pipe, and discharged 
through a 3-inch hose about 50 feet in length. The hose was pro¬ 
vided with a nozzle 3 feet in length and 2 inches in diameter. The 
boiler, engine, pump, and pile-driver were mounted on a platform 
12 feet in width and 24 feet in length.” f 

345. Jet vs. Hammer. It is hardly possible to make a compari¬ 
son between a water-jet and a hammer pile-driver, as the conditions 
most favorable for each are directly opposite. For example, sand 
yields easily to the jet, but offers great resistance to driving with 
the hammer ; on the other hand, in stiff clay the hammer is much 


* Chas. McDonald, in Trans. Am. Soc. of C. E., vol. viii. pp. 227-37. 

+ “ The Water-Jet as an Aid to Engineering Construction,” p. 11a pamphlet 
published (1881) by the Engineer Department of the U. S. Army. 





230 


PILE FOUNDATIONS. 


[CHAP. XI. 


more expeditions. For inland work the hammer is better, owing to 
the difficulty of obtaining the large quantities of water required for 
ihe jet; but for river and harbor work the jet is the most advan¬ 
tageous. Under equally favorable conditions there is little or no 
difference in cost or speed of the two methods.* 

The jet and the hammer are often advantageously used together, 
especially in stiff clay. The efficiency of the water-jet can be greatly 
increased by bringing the weight of the pontoon upon which the 
machinery is placed, to bear upon the pile by means of a block and 
tackle. 

346. Cost of Piles. At Chicago and at points on the Missis¬ 
sippi above St. Louis, pine pile', cost from 10 to 15 cents per lineal 
foot, according to length and location. Soft-wood piles, including 
rock elm, can be had in almost any locality for 8 to 10 cents per 
foot. Oak piles 20 to 30 feet long cost from 10 to 12 cents per 
foot; 30 to 40 feet long, from 12 to 14 cents per foot; 40 to 60 
feet long, from 20 to 30 cents per foot. 

347. Cost of Pile Delving. There are many items that affect 
the cost of work, which can not be included in a brief summary, but 
which must not be forgotten in using such data in making estimates. 
Below are the details for the several classes of work. 

348. Railroad Construction. The following table is a summary 
of the cost, to the contractor, of labor in driving piles (exclusive of 
hauling) in the construction of the Chicago branch of the Atchison, 
Topeka and Santa Fe R. R. The piles were driven, ahead of the 
track, with a liorse-power drop-hammer weighing 2,200 pounds. 
The average depth driven was 13 feet. The table includes the 
cost of driving piles for abutments for Howe truss bridges and 
for the false work for the erection of the same. These two items 
add considerably to the average cost. The contractor received 
the same price for all classes of work. The work was as varied as 
such jobs usually are, piles being driven in all kinds of soil. Owing 
to the large amount of railroad work in progress in 1887, the cost 
of material and labor was about 10 per cent, higher than the aver¬ 
age of the year before and after. Cost of labor on pile-driver: 1 
foreman at $4 per day, 6 laborers at $2, 2 teams at $3.50; total cost 
of labor = $23 per day. 


* Report of Chief of Engineers U. S. A., 1883, pp. 1264-73. 





AM. 1.] DESCRIPTIONS, AND METHODS OF DRIVING. 


231 


Cost of Pile Driving in Railroad Construction. 


Number of piles included in this report. 4,409 

“ “ liueal feet included in this report. 109,568 

Average length of the piles, in feet. 24.8 

Number of daj^s employed in driving. 494 

“ “ lineal feet driven per day. 221.8 

Cost of driving, per pile... $2.53 

“ “ “ “ foot. 10.4 cents. 


349. Railroad Repairs. The following are the data of pile 
driving for repairs to bridges on the Indianapolis, Decatur and 
Springfield R. R. The work was done from December 21, 1885, to 
January 5, 1886. The piles varied from 12 to 32 feet in length, 
the average being a little over 21 feet. The average distance driven 
was about 10 feet. The hammer weighed 1,650 pounds; the last 
fall was 37 feet, and the corresponding penetration did not exceed 
2 inches. The hammer was raised by a rope attached to the draw¬ 
bar of a locomotive—comparatively a very expensive way. 

TABLE 26. 

Cost of Piles for Bridge Repairs. 


Items of Expense. 

Total. 

Per Pile. 

Per Foot. 

T nhnv • T nnrlinrr iinrl nnlnarlinp - r>iles. 7U. r1a.VS. 

$16.00 

153.75 

45.90 

71.50 

23.49 

13.29 

11.04 

$0.08 

0.78 

0.23 

0.37 

0.13 

0.06 

0.05 

0.4 cts. 
3.7 

1.1 

1.6 

0.5 

0.3 

0.3 

UriHc-#* cmncr flrivinpv 12 davs . 

Engine crew, transportation and driving, 13 days.. 
Train crew, “ “ “ “ . 

i/n / nlip& • Tfino-inp. survnliftS... 

fi nilf> rinp^s a.nrl 2 nla.tes. 

"Renalrs .. 

' Tnfn.l. pnr.Y)pn.Rp. fov clvivilin . 

$334.97 

$1.70 

7.9 cts. 

Hfnter'irtl • 4 192 feet nalr niles at 13U> Cts. 

$565.92 

$2.86 

13.5 cts. 

Tot a n cost ... 

$900.69 

$4.56 

21.4 cts. 



On the same road, 9 piles, each 20 feet long, were driven 9 feet, 
for bumping-posts, with a 1,650-pound hammer dropping 17 feet. 
The hammer was raised with an ordinary crab-winch and single 
line, with double crank worked by four men. The cost for labor was 
8.3 cents per foot of pile, and the total expense was 21.8 cents per foot. 

350. Bridge Construction. The following table gives the cost 
of labor in driving the piles for the Northern Pacific R. R. bridge 
over the Red River, at Grand Forks, Dakota, constructed in 1887. 
The soil was sand and clay. The penetration under a 2,250-pound 
hammer falling 30 feet was from 2 to 4 inches. The foreman re* 
eeived $5 per day, the stationary engineer $3.50, and laborers $2. 








































232 


PILE FOUNDATIONS. 


[CHAP. XI„ 


TABLE 27 

Cost of Labor in Driving Piles in Bridge Construction. 


Kind of Labor. 

Pile Bridge on 

Land. 

Temporary 

Bridge. 

Draw Fender 

and 

Ice Breaker. 

Pivot Pier. 

River Pier. 

Preparation and repair of plant. 

Driving . . 

$68.95 

432.70 

78.75 

$63.65 

252.92 

$53.50 

430.50 

47.50 

$37.00 

215.45 

179.80* 

$61.60 
565.80 
131 90t 

Sawing and straightening. 

Total cost. 

$580.40 

$316.57 

$531.50 

$432.25 

$759.30 

Number of piles in the structure. 

Total number of feet remaining in the structure.. 
Average length of piles “ “ “ “ 

Average length of piles cut off. 

Cost per foot of pile remaining in the structure... 

224 

7,238 

32.3 

1.1 

102 

3,710 

104 

7,023 

38.2 

4.1 

121 

4,639 

38.4 

6.6 

167 

7,316 

43.8 

3.7 

8.0 cts. 

8.5 cts. 

7.6 cts. 

9.3 cts. 

10.4 cts. 


Average cost for driving, per foot remaining in the structure = 8.8 cents. 

* Sawed off under 8 feet of water. 

t Including $70.25 for excavating and bailing in order to get at the sawing. 

351. Foundation Piles. The contract price for the foundation 
piles—white oak—for the railroad bridge over the Missouri River, at. 
Sibley, Mo., was 22 cents per foot for the piles and 28 cents per foot 
for driving and sawing off below water. They were 50 feet lcng, 
and were driven in sand and gravel, in a coffer-dam 16 feet deep, 
by a drop-hammer weighing 3,203 pounds, falling 36 feet. The ham¬ 
mer was raised by steam power. . 

352. In the construction of a railroad in southern Wisconsin 
during 1885-87, the contract price—the lowest competitive bid—for 
the piles, in place, under the piers of several large bridges averaged 
as in the following table. The piles were driven in a strong current 
and sawed off under water, hence the comparatively great expense. 

TABLE 28. 

Contract Price of Foundation Piles. 


Material of Pile. 

Kind of Driving. 

Contract Price 

For Part remaining in 
Structure. 

per Lineal Foot. 

For Pile Heads Sawed 
off. 

Rock Elm 

Ordinary 

40 cents 

15 cents 

Pine 

i i 

40 “ 

20 “ 

Oak 

H 

48 “ 

25 “ 

Oak 

Hard 

50 “ 

30 “ 



























































ART. 2 .] 


BEARING POWER OF PILES. 


233 


353. In 1887 the contract price for piles in the foundations of 
bridge piers in the river at Chicago was 35 cents per foot of pile 
left in the foundation. This prief* covered cost of timber (10 to 15 
cents), driving, and cutting off 12 to 14 feet below the surface of 
the water,—about 17 feet being left in the foundation. 

The cost of driving and sawing off may be estimated about 
as follows : (17 -j- 13) feet of pile at 13 cents per foot = $3.90 ; 17 
feet of pile, left in the structure, at 35 cents per foot = $5.95. 
$5.95 — $3.90 = $2.05 = the cost per pile of driving and sawing off, 
which is equivalent to nearly 7 cents per foot of total length of pile. 
In this case the waste or loss in the pile heads cut off adds consider¬ 
ably to the cost of the piles remaining in the structure. In mak¬ 
ing estimates this allowance should never be overlooked. 

354. Harbor and River Work. In the shore-protection work at 
Chicago, done in 1882 by the Illinois Central R. R., a crew of 9 
men, at a daily expense, for labor, of $17.25, averaged 65 piles per 10 
hours in water 7 feet deep, the piles being 24 feet long and being 
driven 14 feet into the sand. The cost for labor of handling, sharp¬ 
ening, and driving, was a little over 26 cents per pile, or 1.9 cents 
per foot of distance driven, or 1.1 cents per foot of pile.* Both 
steam-hammers and water-jets were used, but not together. Notice 
that this is very cheap, owing (1) to the use of the jet, (2) to little 
loss of time in moving the driver and getting the pile exactly in the 
predetermined place, (3) to the piles not being sawed off, and (4) 
to the skill gained by the workmen in a long job. 

On the Mississippi River, under the direction of the U. S. 
Army engineers, the cost in 1882 for labor for handling, sharpen¬ 
ing, and driving, was $3.11 per pile, or 20 cents per foot driven. 
The piles were 35 feet long, the depth of water 15.5 feet, and the 
depth driven 13.6 feet. The water-jet and drop-hammer were used 
together. The large cost was due, in part at least, to the current, 
which was from 3 to 6 miles per hour.f 

Art. 2. Bearing Power of Piles. 

355. Two cases must be distinguished ; that of columnar piles or 
those whose lower end rests upon a hard stratum, and that of ordi¬ 
nary bearing piles or those whose supporting power is due to the 

* Report of the Chief of Engineers, U. S. A., for 1883, pp. 1266-7(L 
t Ibid., p. 1260. 






234 


PILE FOUNDATIONS. 


[CHAP. XI. 


friction of the earth on the sides of the pile. In the first case, the 
bearing power is limited by the strength of the pile considered as a 
column ; and, since the earth prevents lateral deflection, at least to 
a considerable degree, the strength of such a pile will approximate 
closely to the crushing strength of the material. This class of piles 
needs no further consideration here. 

356. Methods of Determining Supporting Power. There 
are two general methods of determining the sujiporting power of 
ordinary bearing piles: first, by considering the relation between the 
supporting power and the length and size of the pile, the weight of 
the hammer, height of fall, and the distance the pile was moved by 
the last blow ; or, second, by applying a load or direct pressure to 
each of a number of piles, observing the amount each will support, 
and expressing the result in terms of the depth driven, size of pile, 
and kind of soil. The first method is applicable only to piles driven 
by the impact of a hammer ; the second is applicable to any pile, 
no matter how driven. 

1. If the relation between the supporting power and the length 
and size of pile, the weight of the hammer, the height of fall, 
and the distance the pile was moved by the last blow can be stated 
in a formula, the supporting power of a pile can be found by insert¬ 
ing these quantities in the formula and solving it. The relation 
between these quantities must be determined from a consideration 
of the theoretical conditions involved, and hence such a formula is 
a rational formula. 

2. By applying the second method to piles under all the con¬ 
ditions likely to occur in practice, and noting the load supported, 
the kind of soil, amount of surface of pile in contact with the soil, 
etc., etc., data could be collected by which to determine the sup¬ 
porting power of any pile. A formula expressing the supporting 
power in terms of these quantities is an empirical formula. 

357. Rational Formulas. The deduction of a rational for¬ 
mula for the supporting power of a pile is not, strictly, an appro¬ 
priate subject for mathematical investigation, as the conditions can 
not be expressed with mathematical precision. However, as there 
is already a great diversity of formulas in common use, which give 
widely divergent results, a careful investigation of the subject is 
necessary. 

The present practice in determining the bearing power of piles is 



I 


ART. 2.] 


BEARING POWER OF PILES. 


235 


neither scientific nor creditable. Many engineers, instead of in¬ 
quiring into the relative merits of the different formulas, take an 
average of all the formulas they can find, and feel that they have a 
result based on the combined wisdom of the profession. This prac¬ 
tice is exactly like that of the ship’s surgeon who poured all his 
medicines into a black jug, and whenever a sailor was ailing gave 
him a spoonful of the mixture. Other engineers, knowing the great 
diversity and general unreliability of the formulas, reject them 
all and trust to their own experience and judgment. The self- 
reliant engineer usually chooses the latter course, while the timid 
one trusts to the former. 

To correctly discriminate between the several formulas, it is 
necessary to have a clear understanding of all the conditions in¬ 
volved. The object of the following discussion is to discover the 
general principles which govern the problem. 

358. When the ram strikes the head of the pile, the first effect 
is to compress both the head of the pile and the ram. The more 
the ram and pile are compressed the greater the force required, until 
finally the force of compression is sufficient to drive the pile through 
the soil. The amount of the pressure on the head of the pile when 
it begins to move, is what we wish to determine. 

To produce a formula for the pressure exerted upon the pile by 
the impact of a descending weight, let 
W = the weight of the ram, in tons; 
w = “ “ “ pile “ 

S = the section of the ram, in sq. ft.; 
s = “ “ “ pile “ “ 

L — the length of the ram, in feet; 
l — “ “ “ pile “ 

E — the co-efficient of elasticity of the ram, in tons per sq. ft. ; 


e = 
h 
d 


(( 


a 


(C 


(( 


e< 


pile 


a 


a (( a 


P = 


the height of fall, in feet ; 

the penetration of the pile, i. e., the distance the pile is 
moved by the last blow, in feet. The distance d is the 
amount the pile as a whole moves, and not the amount 
the top of the head moves. This can be found accu¬ 
rately enough by measuring the movement of a point, 
say, 2 or 3 feet below the head, 
the pressure, in tons, which will just move the pile the very 








236 


PILE FOUNDATIONS. 


[CHAP. XI- 


small distance d ,—that is to say, the pressure produced 
by the last blow; or, briefly, P may be called the sup¬ 
porting power. 

Then Wh is the accumulated energy of the ram at the instant it 
strikes the head of the pile. This energy is spent (1) in compress¬ 
ing the ram, (2) in compressing the head of the pile, (3) in moving 
the pile as a whole against the resistance of the soil, (4) in overcom¬ 
ing the inertia of the pile, (5) in overcoming the inertia of the soil 
at the lower end of the pile, and (C) by the friction of the ram 
against guides and air. These will be considered in order. 

1. The energy consumed in compressing the hammer is repre¬ 
sented by the product of the mean pressure and the compression, or 
shortening, of the ram. The pressure at any point in a striking 
weight varies as the amount of material above that point; that is to 
say, the pressure at any point of the hammer varies inversely as its 
distance from the lower surface. The pressure at the lower surface 
is P, and that at the upper one is zero ; hence the mean pressure 
is i P. From the principles of the resistance of materials, the com¬ 
pression, or the shortening, is ^-=y, in which p is the uniform pres- 

O Uj 


sure. From the above, p = ^ P. Consequently the shortening is 

1 PL 

2 SE' 

If the fibers of the face of the ram are not seriously crushed, the 
mean pressure will be one half of the maximum pressure due to im¬ 
pact ; or the mean pressure during the time the ram and pile are 

1 P 2 L 

being compressed is \ P. Then the energy consumed is-——. 

The yielding of the material of the ram is probably small, and might 
be omitted, but as it adds no complication, as will presently appear, 
it is included. 

2. The mean pressure on the head of the pile is i P, as above. 
For simplicity assume that the pile is of uniform section through¬ 
out. To determine the shortening, notice that for the part of the 
pile above the ground the maximum pressure is uniform through¬ 
out, but that for the part under the surface the maximum pressure 
varies as some function of the length. If the soil were homogeneous, 
the pressure would vary about as the length in the ground ; and 





ART. 2 .] 


BEARING POWER OF‘PILES. 


237 


hence the shortening would be — —. But, remembering that the- 

resistance is generally greater at the lower end than at the upper, 
and that any swaying or vibration of the upper end will still further 
diminish the resistance near the top, it is probable that the mean 
pressure is below the center. It will here be assumed that the mean 
pressure on the fibers of the pile is two thirds of that on the head. 


2 pi 

which is equivalent to assuming that the shortening is — —, when 

the pile is wholly immersed. If only a part of the pile is in contact 

with the soil, the shortening will be = — (V -j- / V 

in which V is the exposed portion and /, the part immersed. For 
simplicity in the following discussion the shortening of the pile- 


will be taken at — —. If a formula is desired for the case when 

3 se 

the top projects above the ground, it will only be necessary to sub¬ 
stitute ( l ' + | for l in equations (1) and (2) below. 

IP 2 / 

Then the energy lost in the compression of the pile is —-. 

o SO 

3. The energy represented by the penetration of the pile is P d . 

4. In the early stage of the contact between the ram and the 
pile, part of the energy of the ram is being used up in overcoming the 
inertia of the pile ; but in the last stage of the compression, this 
energy is given out by the stoppage of the pile. At most, the effect 
of the inertia of the pile is small; and hence it will be neglected. 

5. The energy lost in overcoming the inertia of the soil at the 
lower end of the pile will vary with the stiffness of the soil and with 
the velocity of penetration. It is impossible to determine the amount 
of this resistance, and hence it can not be included in a formula. 
Omitting this element causes the formula to give too great a support¬ 
ing power. The error involved can not be very great, and is to be 
covered by the factor of safety adopted. 

6. The friction of the ram against the guides and against the air 
diminishes the effect of the blow, but the amount of this can not be 
computed. Omitting this element will cause the formula for the 
supporting power to give too great a result. The friction against 
the air increases very rapidly with the height of fall, and hence the 









238 


PILE FOUNDATION’S. 


[CHAP. XI t 


smaller the fall the more nearly will the formula give the true sup¬ 
porting power. 

359. Equating the energy of the falling weight with that con¬ 
sumed in compressing the pile and ram, and in the penetration of 
the pile, as discussed in paragraphs 1, 2, and 3 above, we have 



• • ( 1 ) 


Solving equation (1) gives 



• ( 2 ) 


3 Lse-\-4:lSE' 


An examination of equation (2) shows that the pressure upon the 
pile varies with the height of fall, the weight, section, length, and 
co-efficient of elasticity of both ram and pile, and with the penetra¬ 
tion. It is easy to see that the weight of the ram and the height 
of the fall should be included. The penetration is the only element 
which varies with the nature of the soil, and so of course it also 
should be included. It is not so easy to see that the length, section, 
and co-efficient of elasticity of the material of the pile and ram 
should be included. If any one will try to drive a large nail into 
hard wood with a piece of leather or rubber intervening between 
the hammer and the head of the nail, he will be impressed with the 
fact that the yielding of the leather or rubber appreciably diminishes 
the effectiveness of the blow. Essentially the same thing occurs in 
trying to drive a large nail with a small hammer, except that in this 
case it is the yielding of the material of the hammer which dimin¬ 
ishes the effect of the blow. In driving piles, the materials of the 
pile and ram act as the rubber in the first illustration; and, reason¬ 
ing by analogy, those elements which determine the yielding of the 
materials of the pile and ram should be included in the formula. 
Obviously, then, the pressure due to impact will be greater the 
harder the material of the pile. Notice also that if the head of the 
pile is bruised, or “ broomed/’ the yielding will be increased; and, 
sconsequently, the pressure due to the blow will be decreased. 











ART. 2.] 


BEARING POWER OF PILES. 


23& 


360. The Author’s Formula for Practice. To simplify equation 
(2), put 


6 S E s e 

3 Lse + i l S E~ q ’ 


and then equation (2) becomes 

P=V‘Zq Wh + q'cT-qd. .... (3) 

Equation (3) can be simplified still further by computing q for 
the conditions as they ordinarily occur in practice. Of course, in 
this, case it will only be possible to assume some average value for 
the various quantities. Assume the section of the pile to be 0.8 sq. 
ft.; the section of the ram, 2 sq. ft.; the length of the ram, 2.5 ft.; 
the length of the pile,* 25 ft.; -the co-efficient of elasticity of the 
ram, 1,080,000 tons per sq. ft.; and the co-efficient of elasticity of 
the pile, 108,000 tons per sq. ft. (an average value for oak, elm, 
pine, etc., but not for palmetto and other soft woods). Computing 
the corresponding value of q, we find it to be 5,1G0; but to secure 
round numbers, we may take it at 5,000, which also gives a little 
additional security. 

Equation (3) then becomes 


P = 100 (V W h + (50 dy- 50 d), . . . (4) 

which is the form to be used in practice. 

Equation (4) is approximate because of the assumptions made in 
deducing equation (1), and also because of the average value taken 
for q\ but probably the error occasioned by these approximations is 
not material. 

361. Notice that, since the co-efficient of elasticity of sound 
material was used in deducing the value of q, equation (4) is to be 
applied only on condition that the last blow is struck upon sound 
wood; and therefore the head of the test pile should be sawed off so 
as to present a solid surface for the last, or test, blow of the hammer. 
(This limitation is exceedingly important.') Since the penetration 
per blow^ can be obtained more accurately by taking the mean dis¬ 
tance for two or three blows than by measuring the distance for a 
single one, it is permissible to take the mean penetration of two or 

* The quantity to be used here is the length out of the ground plus about two 
thirds of the part in the ground (see paragraph 2 of § 353). 









240 


PILE FOUNDATIONS. 


[CHAP. XI. 


three blows; but their number and force should be such as not to 
crush the head of the pile. 

In this connection the following table, given by Don. J. Whitte- 
more, in the Transactions of the American Society of Civil Engi¬ 
neers, vol. xii. p. 442, to show the gain in efficiency of the driving 
power by cutting off the bruised or broomed head of the pile, is very 


instructive. The pile was of green Norway pine; the 
the Nasmyth type, and weighed 2,800 pounds. 

ram was 

Table showing the Gain in Efficiency of 
Cutting off the Broomed Head 

the Driving 
of the Pile. 

t Power 

3d ft. of penetration required 


... 5 

blows. 

4th “ 



a 

5th “ 



i ( 

6th “ “ 


... 29 

i i 

7th “ 



i i 

8th “ 

• • 

... 46 

i i 

9th “ “ 


... 61 

< < 

10th “ 



6 i 

11th “ 


... 109 

(( 

12th “ 



it 

13th “ “ 


... 257 

< t 

14th “ 



< t 

Head of the pile adzed off. 

15th ft. of penetration required 



it 

16th “ “ “ 


... 572 

it 

17th “ 


... 832 

t t 

18th “ 



it 

Head of the pile adzed off. 

19th ft. of penetration required 


... 213 

t ( 

20th “ 



< t 

21st “ 



€€ 

22d “ 

Total number of blows, . 


. . . 5,228 

it 


Notice that the average penetration per blow was 2£ times greater 
during the 15th foot than during the 14th; and nearly 4 times 
greater in the 19th than in the 18th. It does not seem unreason¬ 
able to believe that the first blows after adzing the head off were 
’Correspondingly more effective than the later ones; consequently, 
it is probable that the first blows for the 15th foot of penetration 
were more than 5 times as efficient as the last ones for the 14th foot, 
and also that the first blows for the 19th foot were 8 or 10 times 
more efficient than the last ones for the 18th foot. Notice also that 
since the head was only “ adzed off/’ it is highly probable that the 
spongy wood was not entirely removed. 
























ART. 2.J 


BEARING POWER OF PILES. 


241 


If the penetration for the last blow before the head was adzed off 
were used in the formula, the apparent supporting power would be 
very much greater than if the penetration for the first blow after 
adzing off is employed. This shows how unscientific it is to pre¬ 
scribe a limit for the penetration without specifying the accompany¬ 
ing condition of the head of the pile, as is ordinarily done. 

362. Weisbach’s Formula. Equation (2), page 238, is essentially 
equivalent to Weisbach’s formula for the supporting power of a pile. 
Weisbach assumes that the pressure is uniform throughout, and 
obtains the formula* 

HIT 


P = 


u + B u 


Vz fff-) h W+cT-d}, . (5) 


in which H = and H x = -j. 

363. Rankine’s Formula. Equation (2), page 238, is also essen¬ 
tially equivalent to Rankine’s formula; and differs from it, only 
because he assumes the pressure to vary directly as the length of 
the pile, and neglects the compression of the ram. Rankine’s 
formula is f _ 


. /4 Whse 4 c! s* e 1 2 dse 

p = V—j— + —f -—’ 



Equation (2) differs from Weisbach’s and Rankine’s on the safe 
side. 

364. Empirical Formulas. General Principles. (1) An empiri¬ 
cal formula should be of correct form; (2) the constants in it should 
be correctly deduced ; and (3) the limits within which it is applica¬ 
ble should be stated. 

For example, suppose that it were desired to determine the 
equation of the straight line A B, Eig. 57. 

Since the given line is straight, we will as¬ 
sume that the empirical formula is of the 
form y — m x. We might find in by measur¬ 
ing the ordinates 1, 2, 3, and place m equal 
tfj their mean. If 1, 2, 3, be the numerical 
values of the respective ordinates, the for¬ 
mula becomes y — 2 x, which gives the line 
0 C. The mean ordinate to 0 C is equal to 
the mean ordinate to A B, but the two are not by any means the 

* Mechanics of Engineering, 6th ed. (Coxe’s Translation), p. 701 
t Civil Engineering, p. 602. 






















2 42 


PILE FOUNDATIONS. 


[CHAP. XI- 



B 


same line. It is evident that this empirical formula is of the wrong 
form. 

For another illustration, assume that some law is correctly repre¬ 
sented by the curve A B, Fig. 58. The form 
of the empirical formula may be such as to 
give the curve CD. These curves coincide 
c exactly at two points, and the mean ordinate 
to the two is the same. To use a com¬ 
mon expression, we may say that, “on the 
average, the empirical formula agrees exactly 
fig. 58. with the facts but it is, nevertheless, not 

even approximately true. The constants were not correctly de¬ 
duced. 

Even if of the correct form and correctly deduced, an empirical 
formula can be safely applied only within the 
limits of those values from which it was deter¬ 
mined. For example, a law may be repre¬ 
sented by the curve A B, Fig. 59. From w 
observations made in the region C E, the em- fig. 59. 

pirical formula has been determined, which gives the curve C E D, 
which between the limits C and E is all that can be desired, but 
which is grossly in error between the limits E and D. To use an 
empirical formula intelligently, it is absolutely necessary that the 
limits within which it is applicable should be known. 

Of course, the observations from which the empirical formula 
was deduced can not be used to test the correctness of the formula; 
such a procedure can check only the mathematical work of deriving 
the constants. 

Elementary as the preceding principles are, many empirical 
formulas are worthless owing to a disregard of these conditions in 



deducing them. 

365. Comparison of Empirical Formulas. We will now briefly 

consider the empirical formulas that are most frequently employed 
to determine the supporting power of piles. * 

HaswelVs formula for the dynamic effect of a falling body is f 
P — 4.426 W V, “as deduced from experiments.” 

The experiments consisted in letting a weight of a few ounces 


* For explanation of the nomenclature, see p. 235. 
t Haswell’s Engineers’ and Mechanics’ Pocket-Book, p. 419. 










ART. 2.] 


BEARING POWER OF PILES. 


243 


fall a few inches upon a coiled spring; and hence the formula is 
entirely inapplicable to pile driving, 

Beaufoy s formula is P = 0.5003 W J 2 , “as determined by 
experiment. Ibis formula was deduced under the same conditions 
as Haswell’s, and hence is useless for pile driving. The difference 
between the formulas is due to the fact that Has well used only one 
weight and one spring, and varied the height of the fall, while Beau¬ 
foy employed one weight and springs of such relative stiffness as 
would stop the weight in nearly the same distance for different 
heights of fall.* * * § Notice that Haswell’s, and also Beaufoy’s formula, 
would give the same bearing power for all soils, other things being 
the same. 


Mystrom’sformula f is P = 


W 3 h 

{Wf-wfcV 


In a later book,J Nys- 


3 W h 

tromgives the formula P = - -j- 9 assuming that “about 25 per 

cent, of the energy of the ram is lost by the crushing of the head of 
the pile.” Both of these formulas are roughly approximate, theo¬ 
retical formulas, although frequently cited as “practical formulas.” 

W 2 h 

Mason’s formula § is P = ^ As in the preceding 

cases, this is frequently referred to as a “ practical formula ;” but an 
examination of the original memoir shows that it is wholly a theo¬ 
retical formula with no pretensions of being anything else. It is 
also sometimes referred to as having been “ tested by a series of 
experiments ;” but apparently the only basis for this is that the 
piles upon which Fort Montgomery (Rouse’s Point, N. Y.) stood 
from 1846 to 1850 without any sign of failure, when tested by this 
formula, showed a co-efficient of safety of 3 T 6 ¥ . The evidence is not 
conclusive: (1) the factor is large enough to cover a considerable 
error in the formula; (2) since the formula assumes that all of the 
energy in the descending ram is expended in overcoming the resist¬ 
ance to penetration, the computed bearing power is too small, and 
consequently the co-efficient of safety is even greater than as stated; 


* Van Nostrand’s Engin’g Mag., vol. xvii. p. 325. 

f Nystrom’s Pocket-Book, p. 158. 

X New Mechanics, p. 134. 

§ Resistance of Piles, J. L. Mason, p. 8; No. 5 of Papers on Practical Engineering, 
published by the Engineering Department of the U. S. Army. 









244 


PILE FOUNDATION'S. 


[CHAP. XI. 


and (3) it is probably safe to say that after a pile has stood a short 
time its bearing power is greater than at the moment the driving 
ceased, owing to the settlement of the earth about it. 

W h 

Sander’s formula* is P f — . , in which P' is the safe bear- 

o Cl 

ing power. This formula was deduced on the assumptions that the 

energy of the falling weight was wholly employed in forcing the 

pile into the ground,— i. e., on the assumption that P d = W h, or 

W h * 

P = ——,—and that the safe load was one eighth of the ultimate 

supporting power. It is therefore a roughly approximate, theoreti¬ 
cal formula. 

Notice that, since some of the energy is always lost, P d, the 
energy represented by the movement of the pile, must always be 
less than W h, the energy of the hammer; hence, P is always less 
Wh . . « . W/i 


than———; or, in mathematical language, P< 

Cl 


d 


This relation is 


very useful for determining the greatest possible value of the sup- 

Wh 


porting power. P will always be considerably less than- 


d 


and 


this difference is greater the lighter the weight, the greater the 
fall, the softer the material of the pile, or the more the head is 
bruised. When d is very small, say £ inch or less, the difference is 
so great as to make this relation useless. 

Trautwine’s formula ,f in the nomenclature of page 235, is 

P ^ 5^, • It was deduced from the observed supporting 

1 + 12 d u b 

power of piles driven in soft soil. Strictly speaking, it is applicable 
onlv under conditions similar to those from which it was deduced: 
and hence it is inapplicable for hard driving and to piles whose 
heads are not bruised about the same amount as were the experi¬ 
mental ones. No formula can be accurate which does not, in some 
way, take cognizance of the condition of the head of the pile. For 
example, experiments Nos. 3 and 4 of the table on page 246 are 
the same except in the condition of the heads of the piles, and yet 


* Jour. Frank. Inst., 3d series, vol. xxii. p. —. 
f Engineer’s Pocket-Book, Ed. 1885, p. 643. 












ART. 2.] 


BEARING POWER OF PILES. 


245 


the load supported by the former was 24 times that supported by the 
latter. This formula is not applicable to piles driven with a steam 
hammer, since according to it the energy represented by the sinking 
of the pile is greater than the total energy in the descending weight. 
For example, if W — 1J tons, h = 2 feet, and d — 1 inch ^ ^ of a 

Wh 

foot, the formula P < —— becomes P < 36 tons. Trautwine’s 

d 


iormula gives P — 49 tons ; that is to say, Trautwine's formula 
makes the supporting power one third more than it would be if no 
energy were lost. 

Engineering News formula * the most recent and the most 


popular, is P' 


2 Wh 


in which P ' is the safe load in tons; and 


d' + 1’ 

d' is the penetration, in inches , under the last blow, which is 
assumed to be appreciable and at an approximately uniform rate. 

366. The Author’s Empirical Formula. Certain assumptions 
and approximations were made in deducing equation (3), page 239. 
If it is thought not desirable to trust entirely to theory, then the 
iormula 


P= V2 q Wh + q*<T - qd .... (7) 


may be considered as giving only the form which the empirical 
formula should have. Under this condition q becomes a numerical 
■co-efficient to be determined by experiment, which must be made 
by driving a pile and measuring d, after which the sustaining power 
must be determined by applying a direct pressure. The last, or 
test, blow should be struck on sound wood. 

367. Table 29 gives all the experiments on the supporting 
power of piles for which the record is complete. Unfortunately 
these experiments do not fulfill the conditions necessary for a proper 
determination of q in equation (7). It is known that in some of the 
cases the head of the pile was considerably broomed, and there is 
internal evidence that this was so in the others. 

The data of the following table substituted in equation (7) give 
values of q from 1.5 to 337, with an average of 130. The range of 
these results shows the inconsistency of the experiments, and the 
smallness of the average shows that the last blow was not struck on 
sound wood. This value of q is of no practical use 


* Engineering News, vo!. xx. pp. 511, 512 (Doc. 29, 1888,. 









246 


PILE FOUNDATIONS. 


[CHAP. XI. 


TABLE 29. 

Data of Experiments on the Supporting Power of Piles. 


Number for 
Reference. 

WEIGHT OF THE 

Hammer, in 
Tons. 

Height of 
Fall, in Feet. 

Penetration, 
in Feet. 

Observed Sup¬ 
porting Pow¬ 
er, in Tons. 

Authority, 

1 

0.455 

5 

0.031 

30.2 

Circular of the Office of Chief of Engineers 
U. S. A., Nov. 12, ’81, pp. 2, 3. 

2 

0.8 

36 

1.5 

7.3 

Trautwine’s Pocket-Book, ed. 1885, p. 643. 

3 

1.12 

30 

0.042 

112.0 

Jour. Frank. Inst., vol. 55, p. 101. 

4 

1.1 

30 

0.042 

45.9 

Delafield’s “Foundations in Compressible Soils,’* 
pp. 17, 18;—a pamphlet published by En¬ 
gineers’ Department of U. S. A. 

5 

0.95 

29 

0.125 

50.0 

Trautwine in Railroad Gazette , July 8, 1887, p. 
453. 


368. As confirming the reliability of the form of equations (3), 
(4), and (7), it is interesting to notice that A. 0. Hertiz* found, 
from the records of the driving and afterwards pulling up of nearly 
400 piles, the following relation : 

7 _Wh P 

d ~ p 500* 

which may be put in the form 

P = V500 Wh + (250 ciy - 250 cl ... . (8) 

Equation (8) has exactly the form of equation (3), page 239, 
although deduced in an entirely different way. The value (250) of 
the constant q in equation (8) is less than that in equation (4), 
page 239, which shows that the heads of the piles were broomed. 
The value of q in equation (8) is greater than that deduced from the 
data of Table 29, which shows that the piles from which equation 
(8) was determined were not bruised as much as those in the above 
table. 

369. Supporting Power Determined by Experiment. It is 

not certain that the bearing power of a pile when loaded with a con¬ 
tinued quiescent load will be the same as that during the very short 

* Proc. Inst, of C. E., vol. lxiy. pp. 311-15 ; republished in Van Nostrand’s Maga¬ 
zine, vol. xxv. pp. 273-76. 





















ART. 2.] 


BEARING POWER OF PILES. 


247 


period of the blow. The friction on the sides of the pile will have 
a greater effect in the former case, while the resistance to penetra¬ 
tion of the point will be greater in the latter. This, and the fact 
that the supporting power of piles sunk by the water-jet can be 
determined in no other way, shows the necessity of experiments to 
determine the bearing power under a steady load. 

Unfortunately no extended experiments have been made in this 
direction. We can give only a collection of as many details as pos¬ 
sible concerning the piles under actual structures and the loads 
which they sustain. In this way, we may derive some idea of the 
sustaining power of piles under various conditions of actual practice. 

370. Ultimate Load. In constructing a light-house at Proctors- 
ville, La. , in 1856-57, a test pile, 12 inches square, driven 29.5 feet, 
bore 29.9 tons without settlement, but with 31.2 tons it “settled 
slowly.” The soil, as determined by borings, had the following 
character : “ For a depth of 9 feet there was mud mixed with 
sand ; then followed a layer of sand about 5 feet thick, next a layer 
of sand mixed with clay from 4 to G feet thick, and then followed 
fine clay. By draining the site the surface was lowered about 6 
inches. The pile, by its own weight, sank 5 feet 4 inches.” The 
above load is equivalent to a frictional resistance of 600 lbs. per 
sq. ft. of surface of pile in contact with the soil. This pile is No. 
1 of the table on page 246. 

At Philadelphia in 1873, a pile was driven 15 ft. into “soft river 
mud, and 5 hours after 7.3 tons caused a sinking of a very small 
fraction of an inch ; under 9 tons it sank f of an inch, and under 
15 tons it sank 5 ft.” The above load is equivalent to 320 lbs. 
per sq. ft. of surface of contact. This pile is No. 2 of the table on 
page 246. 

In the construction of the dock at the Pensacola navy yard, a pile 
driven 16 feet into clean white sand sustained a direct pressure of 
43 tons without settlement, while 45 tons caused it to rise slowly; 
and it required 46 tons to draw a pile that had been driven 16 feet 
into the sand. This is equivalent to a frictional resistance of 1,900 
lbs. per sq. ft. This pile is No. 4 of the table on page 246. 

“In the construction of a foundation for an elevator at Buffalo, 
N. Y., a pile 15 inches in diameter at the large end, driven 18 ft., 
bore 25 tons for 27 hours without any ascertainable effect. The 
weight was then gradually increased until the total load on the 




248 


PILE FOUNDATION'S. 


[CHAP. XI. 


pile was 37^ tons. Up to this weight there had been no depression 
of the pile, but with 37^ tons there was a gradual depression which 
aggregated of an inch, beyond which there was no depression 
until the weight was increased to 50 tons. AVith 50 tons there was 
a further depression of -J of an inch, making the total depression 
1J inches. Then the load was increased to 75 tons, under which 
the total depression reached 3|- inches. The experiment was not 
carried beyond this point. The soil, in order from the top, was- 
as follows : 2 ft. of blue clay, 3 ft. of gravel, 5 ft. of stiff red clay, 

. 2 ft. of quicksand, 3 ft. of red clay, 2 ft. of gravel and sand, and 
3 ft. of very stiff blue clay. All the time during this experiment 
there were three pile-drivers at work on the foundation, thus keep¬ 
ing up a tremor in the ground. The water from Lake Erie had 
free access to the pile through the gravel.”* This is equivalent 
to a frictional resistance of 1,850 lbs. per sq. ft. This is pile No. 5 
of the table on page 246. 

371. In making some repairs at the Hull docks, England,, 
several hundred sheet-piles were drawn out. They were 12 X 10 
inches, driven an average depth of 18 feet in stiff blue clay, and 
the average force required to pull them was not less than 35.8 
tons each. The frictional resistance was at least 1,875 lbs. per sq. 
ft. of surface in contact with the soil, f 

372. Safe Load. The piles under the bridge over the Missouri 
at Bismarck, Dakota, were driven 32 ft. into the sand, and sustain 
20 tons each—equivalent to a frictional resistance of 600 lbs. per sq. 
ft. The piles at the Plattsmouth bridge, driven 28 ft. into the 
sand, sustain less than 13| tons, of which about one fifth is live 
load,—equivalent to a frictional resistance of 300 lbs. per sq. ft. 

At the Hull docks, England, piles driven 16 ft. into “ alluvial 
mud ” sustain at least 20 tons, and according to some 25 tons ; for • 
the former, the friction is about 800 lbs. per sq. ft. The piles 
under the Royal Border bridge “were driven 30 to 40 ft. into sand 
and gravel, and sustain 70 tons each,”—the friction being about 
1,400 lbs. per sq. ft. 

373. “The South Street bridge approach, Philadelphia, fell by 
the sinking of the foundation piles under a load of 24 tons each. 

* By courtesy of John C. Trautwine, Jr., from private correspondence of John EL 
Payne and W. A. Haven, engineers in charge. 
fProc. Inst, of C. E., vol. lxiv. pp. 311-15. 





ART. 2.] 


BEARING POWER OF PILES. 


249 


They were driven to an absolute stoppage by a 1-ton hammer fall¬ 
ing 32 feet. Their length was from 24 to 41 feet. The piles were 
driven through mud, then tough clay, and into hard gravel.”* * * § 
A possible explanation of the failure of these piles is that they 
vibrated under the moving load, which allowed the water to work 
its way down the sides o-f the piles and thus decrease the bear¬ 
ing power ; but it is more probable that the last blow was struck 
on a broomed head, which would greatly reduce the penetration, 
and that consequently their supporting power was overestimated. 
According to Trautwine’s formula—the only one of all the pre¬ 
ceding which is even approximately applicable to this case—their 
supporting power was 164 tons. 

374. Supporting Power of Screw and Disk Piles. The sup¬ 
porting power depends upon the nature of the soil and the depth to 
which the pile is sunk. A screw pile “ in soft mud above clay and 
sand ” supported 1.8 tons per sq. ft. of blade, f A disk pile in 
“ quicksand ” stood 5 tons per sq. ft. under vibrations. J Charles 
McDonald, in constructing the iron ocean-pier at Coney Island, as¬ 
sumed that the safe load upon the flanges of the iron disks sunk into 
the sand, was 5 tons per sq. ft.; but “ many of them really support 
as much as 6.3 tons per sq. ft. continually and are subject to occa¬ 
sional loads of 8 tons per sq. ft., without causing any settlement 
that can be detected by the eye.”§ 

375. FACTOR OF Safety. On account of the many uncertainties 
in connection with piles, a wide margin of safety is recommended by 
all authorities. The factor of safety ranges from 2 to 12 according 
to the importance of the structure and according to the faith in the 
formula employed or the experiment taken as a guide. At best, 
the formulas can give only the supporting power at the time when 
the driving ceases. If the resistance is derived mainly from fric¬ 
tion, it is probable that the supporting power increases for a time 
after the driving ceases, since the co-efficient of friction is usually 
greater after a period of rest. If the supporting power is derived 
mainly from the resistance to penetration of a stiff substratum, the 
bearing power for a steady load will probably be smaller than the 


* Trans. Am. Soc. of C. E., vol. vii. p. 264. 

fProc. Inst, of C. E., vol. xvii. p. 451. 

X Ibid., p. 443. 

§ Trans. Am. Soc. C. E., vol. viii. p. 236. 






250 


PILE FOUNDATIONS. 


[CHAP. Xl. 


force required to drive it, as most materials require a less force to 
change their form slowly than rapidly. If the soil adjoining the 
piles becomes wet, the supporting power will be decreased; and 
vibrations of the structure will have a like effect. 

The formulas in use for determining the supporting power of 
piles are so unreliable, that it is quite impossible to determine the 
factor of safety for any existing structure with anything like accu¬ 
racy. 

The factor to be employed should vary with the nature of the 
structure. For example, the abutments of a stone arch should bo 
constructed so that they will not settle at all; but if a railroad pile 
trestle settles no serious damage is done, since the track can be 
shimmed up occasionally. In a few cases, a small settlement has 
taken place in a railroad trestle when the factor of safety was 3 or 
4, as computed by equation (4), page 239. 

Art. 3. Arrangement of the Foundation. 

376. Disposition of the Piles. The length of the piles to be 
used is .determined by the nature of the soil, or the conveniences 
for driving, or the lengths most easily obtained. The safe bearing 
power maybe determined from the data presented in §§ 370-73, or, 
better, by driving a test pile and applying equation (4), page 239. 
Then, knowing the weight to be supported, and having decided 
upon the length of piles to be used, and having ascertained their 
safe bearing power, it is an easy matter to determine how many piles 
are required. Of course, the number of piles under the different 
parts of a structure should be proportional to the weights of those 
parts. 

If the attempt is made to drive piles too close together, they are 
liable to force each other up. To avoid this, the centers of the 
piles should be, at least, 2} or 3 feet apart. Of course, they mav 
be farther apart, if a less number will give sufficient supporting 
power, or if a greater area of foundation is necessary to prevent 
overturning. 

When a grillage (§ 380) is to be placed on the head of the piles, 
great care must be taken to get the latter in line so that the lowest 
course of grillage timber, in this case called capping, may rest 
squarely upon all the piles of a row. In driving under water, a 



ART. 3.] 


ARRANGEMENT OF THE FOUNDATION. 


251 


convenient way of marking the positions of the piles is to construct 
a light frame of narrow boards, called a spider, in which the posi¬ 
tion of the piles is indicated by a small square opening. This frame 
may be held in place by fastening it to the sides of the coffer-dam, 
or to the piles already driven, or to temporary supports. Under 
ordinary circumstances, it is reasonably good work if the center 
of the pile is under the cap. Piles frequently get considerably out 
of place in driving, in which case they may sometimes be forced 
back with a block and tackle or a jack-screw. When the heads of 
the piles are to be covered with concrete, the exact position of the 
* piles is comparatively an unimportant matter. 

In close driving, it is necessary to commence at the center 
of the area and work towards the sides; for if the central ones are 
left until the last, the soil may become so consolidated that they 
can scarcely be driven at all. 

377. Butt vs. Top Down. According to Kankine* all piles 
should be driven large end down, having first been sharpened to a 
point 1|- to 2 times as long as the diameter of the pile. This is at 
least of doubtful utility. If the pile is supported wholly by fric¬ 
tion, then the supporting power will be greater when the small end 
is down. If the soil is semi-liquid, the buoyancy would be slightly 
greater when the large end is down ; but the buoyancy constitutes 
but a very small part of the supporting power, and the difference 
in buoyancy between top and bottom down is still less. If the pile 
derives its support mainly from a solid substratum, then its bearing 
power would be greater with the large end down ; but, in this case, 
it should not be sharpened. For close driving, it is frequently 
recommended that, to prevent the piles from forcing each other up, 
they should be driven butt end down. Notice, however, that if 
the soil is non-compressible, as pure sand, or if the piles are driven 
so close as to compress the soil considerably, it will rise and carry 
the piles with it, whether they were driven with the big or the little 
end down. Piles are generally driven small end down, but never¬ 
theless practical experience shows that there are conditions in which 
it is apparently impossible to drive them in this way, even in 
comparatively isolated positions. These conditions appear to occur 
most frequently in swamps, and in connection with quicksand. 


* “ Civil Engineering,” p. 602. 





252 


PILE FOUNDATIONS. 


[CHAP. XI. 


378. Sawing-off the Piles. When piles are driven, it is 
generally necessary to saw them off either to bring them to the 
same height, or to get the tops lower than they can be driven, or to 
secure sound wood upon which to rest the timber platform that 
carries the masonry. When'above water, piles are usually sawed off 
by hand ; and when below, by machinery—usually a circular saw on 
a vertical shaft held between the leaders of the pile driver or mounted 
upon a special frame, and driven by the engine used in driving the 
piles. The saw-shaft is sometimes attached to a vertical shaft held 
between the leaders by parallel bars, by which arrangement the saw 
can be swung in the arc of a circle and several piles be cut off with¬ 
out moving the machine. The piles are sometimes sawed off with 
what is called a pendulum saw, i.e ., a saw-blade fastened between 
two arms of a rigid frame which extends into the water and is free 
to swing about an axis above. The saw is swung by men pushing 
on the frame. The first method is the better, particularly when 
the piles are to be sawed off under mud or silt. 

Considerable care is required to get the tops cut off in a hori¬ 
zontal plane. It is not necessary that this shall be done with mathe¬ 
matical accuracy, since if one pile does stand up too far the excess 
load upon it will either force it down or crush the cap until the 
other piles take part of the weight. Under ordinary conditions, it 
is a reasonably good job if piles on land are sawed within half an 
inch of the same height; and under water, within one inch. When 
a machine is used on land, it is usually mounted upon a track and 
drawn along from pile to pile, by which device, after having leveled 
up the track, a whole row can be sawed off with no further atten¬ 
tion. When sawing under water, the depth below the surface is 
indicated by a mark on the saw-shaft, or a target on the saw- 
shaft is observed upon with a leveling instrument, or a leveling rod 
is read upon some part of the saw-frame, etc. In sawing piles off 
under water, from a boat, a great deal of time is consumed (par¬ 
ticularly if there is a current) in getting the boat into position 
ready to begin work. 

Piles are frequently sawed off under 10 to 15 feet of water, and 
occasionally under 20 to 25 feet. 

379. Finishing the Foundation. There are two cases: (1) 
when the heads of the piles are not under water ; and (2) wheu they 
are under water. 





ART. 3.] 


ARRANGEMENT OF THE FOUNDATION. 


253 


1. When the piles are not under water there are again two cases : 
(g) when a timber grillage is used ; and ( b ) when concrete alone is 
used. 

2. When the piles are sawed off under w T ater, the timber struct¬ 
ure (in this case called a crib) which intervenes between the piles 
and the masonry is put together first, and then sunk into place. The 
construction is essentially the same as when the piles are not under 
water, but differs from that case in the manner of getting the tim¬ 
ber into its final resting place. The methods of constructing foun¬ 
dations under water, including that by the use of timber cribs, will 
be discussed in Art. 2 of the next chapter. 

380. Piles and Grillage. This is a stout frame of one or more 
courses of timber drift-bolted or pinned to the tops of the piles 
and to each other, upon which a floor of thick boards is placed to 
receive the bottom courses of masonry. Tor illustrated examples, 
see Fig. 84, page 3G2, Fig. 86, page 380, and Fig. 90, page 386. 

The timbers which rest upon the heads of the piles, called caps, 
are usually about 1 foot square, and are fastened by boring a hole 
through each and into the head of the pile and driving into the 
hole a plain rod or bar of iron having about 25 per cent, larger cross 
section than the hole. 

381. These rods are called drift-bolts, and are usually either 
a rod 1 inch in diameter (driven into a f-inch auger hole), or a 
bar 1 inch square (driven into a -J-inch hole). Formerly jag-bolts( 
or rag-bolts, i. e., bolts whose sides were jagged, or barbed, were 
used for this and similar purposes; but universal experience shows 
that smooth rods hold much the better. In some experiments 
made at the Poughkeepsie bridge (§ 414), it was found that a 1-inch 
rod driven into a ff-inch hole in hemlock required on the average 
a force of 2J tons per linear foot of rod to withdraw it; and a 1-inch 
rod driven into a f-inch hole in white or Norway pine required 
5 tons per linear foot of rod to withdraw it.* The old-style jag- 
bolt was square because it was more easily barbed ; and probably 
this is the reason why square drift-bolts are now more common. 
Another advantage of the round drift-bolt, over the square one, is 
that the latter does not cut or tear the wood as much as the former. 
The ends of the rods should be slightly rounded with a hammer. 

Transverse timbers are put on top of the caps and drift-bolted 
to them. Old bridge- timbers, timbers from false works, etc., are 


* For additional data, see Note 8, page 547. 






254 PILE FOUNDATION'S. [CHAP. XI. 

frequently used, and are ordinarily as good for this purpose as new. 
As many courses may be added as is necessary, each perpendicular 
to the one below it. The timbers of the top course are laid close 
together, or, as before stated, a floor of thick boards is added on top 
to receive the masonry. 

This form of construction is very common in the foundations of 
bridge abutments. Of course no timber should be used in a foun- 
'dation, except where it will always be wet. 

382. Piles and Conckete. A thick layer of concrete, resting 
partly on the heads of the piles and partly on the soil between 
them, is frequently employed instead of the timber grillage as above. 
Objection is sometimes made to the platform (§ 380) as a bed for a 
foundation that, owing to the want of adhesion between wood and 
mortar, the masonry might slide off from the platform if any un¬ 
equal settling should take place. To obviate this, the concrete is 
frequently substituted for the grillage and platform. 

However, there is but slight probability that a foundation will 
ever fail on account of the masonry’s sliding on timber, since, ordi¬ 
narily, this could take place only when the horizontal force is 
nearly half of the downward pressure.* This could occur only 
with dams, retaining walls, or bridge abutments, and rarely, if 
ever, with these. One of the fundamental principles of all masonry 
construction is to build the courses perpendicular to the line of 
pressure, which condition alone would prevent slipping. Any pos¬ 
sibility of slipping can be prevented also by omitting one or more 
of the timbers in the top course—the omitted timbers being per¬ 
pendicular to the direction of the forces tending to produce sliding, 
•—or by building the top of the grillage in the form of steps, or by 
driving drift-bolts into the platform and leaving their upper ends 
projecting. 

Although the use of concrete, as above, may not be necessary to 
prevent sliding, it adds materially to the supporting power of the 
foundation ; it utilizes the bearing power of the soil between the 
piles as well as the supporting power of the piles themselves, 
which is a very important consideration in soft soils. Another ad¬ 
vantage of this form of construction is that the concrete can be laid 
without exhausting the water or sawing off the piles. Frequently 


* See Table 36, page 315. 





ART. 3.] 


ARRANGEMENT OF THE FOUNDATION. 


255 


concrete can also be used advantageously in connection with timber 
grillage to pack in around the timbers. 

383. Lateral Yielding. Notice that, although the masonry 
may not slide oh from the timber platform (§ 382), the foundation 
may yield laterally by the piles themselves being pushed over. If 
the piles reach a firm subsoil, it will help matters a little to remove 
the upper and more yielding soil from around the tops of the piles 
and till in with broken stone ; or a wall of piles may be driven 
around the foundation—at some distance from it,—and timber 
braces be placed between the wall of piles and the foundation. 
When the foundation can not be buttressed in front, the structure 
may be prevented from moving forward by rods which bear on the 
face of the wall and are connected with plates of iron or blocks of 
stone imbedded in the earth at a distance behind the wall (see 
§ 551), or the thrust of the earth against the back of the wall may 
be decreased by supporting the earth immediately behind the 
foundation proper upon a grillage and platform resting on piles, or 
the same result may be attained by constructing relieving arches 
against the back of the wall (see § 552). 

384. Cushing’s Pile Foundation. The desire to utilize the 
cheapness and efficiency of ordinary piles as a foundation for bridge 
piers and at the same time secure greater durability than is pos¬ 
sible with piles alone, led to the introduction of what is known as 
Cushing’s pile foundation, first used in 1868, at India Point, Rhode 
Island. It consists of square timber piles in intimate contact with 
each other, forming a solid mass of bearing timber. Surrounding 
the pile cluster is an envelope of cast or wrought iron, sunk in the 
mud or silt only enough to protect the piles, all voids between piles 
and cylinders being filled with hydraulic concrete. 

Several such foundations have been used, and have proved 
satisfactory in every respect. The only objection that has ever 
been urged against them is that the piles may rot above the water 
line. If they do rot at all, it will be very slowly; and time alone 
can tell whether this is an important objection. 

In making a foundation according to the Cushing system, the 
piles may be driven first and the cylinder sunk over them, or the 
piles can be driven inside the cylinder after a few sections are 
in place. In the latter case, however, ‘the cylinders may be sub¬ 
jected to undue strains and to subsequent damage from shock and 



256 


PILE FOUNDATIONS. 


[CHAP. XI. 


vibration; and besides, the sawing off of the piles would be very 
difficult and inconvenient, and they would have to be left at irreg¬ 
ular heights and with battered tops. On the other hand, if the 
piles are driven first, there is danger of their spreading and there¬ 
by interfering with the sinking of the cylinder. 

The .special advantages of the Cushing piers are : (1) cheapness, 
(2) ability to resist scour, (3) small contraction of the water way, 
and (4) rapidity of construction. 

385. Example. The railroad bridge over the Tenas River, near 
Mobile, rests on Cushing piers. There are thirteen, one being a 
pivot pier. Each, excepting the pivot pier, is made of two cast- 
iron cylinders, 6 feet in exterior diameter, located 16 feet between 
centers. The cylinders were cast in sections 10 feet long, of metal 
1J inches thick, and united by interior flanges 2 inches thick and 
3 inches wide. The sections are held together by 40 bolts, each 
If inches in diameter. The lower section in each pier was pro¬ 
vided with a cutting-edge, and the top section was cast of a length 
sufficient to bring the pier to its proper elevation. 

The pivot pier is composed of one central cylinder 6 feet in 
diameter, and six cylinders 4 feet in diameter arranged hexagonally. 
The radius of the pivot circle, measuring from the centers of cylin¬ 
ders, is 12 J feet. Each cylinder is capped with a cast-iron plate 
2 1 inches thick, secured to the cylinder with twenty 1-inch bolts. 

The piles are sawed pine, not less than 10 inches square at the 
small end. They were driven first, and the cylinder sank over 
them. In each of the large cylinders, 12 piles, and in each of the 
smaller cylinders, 5 piles, were driven to a depth not less than 20 
feet below the bed of the river. The piles had to be in almost per¬ 
fect contact for their whole length, which was secured by driving 
their points in contact as near as possible, and then pulling their 
tops together and holding them by 8 bolts 1| inches in diameter. 
In this particular bridge the iron c}dinders were sunk to a depth 
not less than 10 feet below the river bed ; but usually they are not 
sunk more than 3 to 7 feet. The piles were cut off at 1 ow t water, 
the water pumped out of the cylinder, and the latter then filled to 
the top with concrete. 



CHAPTER XII. 


FOUNDATIONS UNDER WATER. 

386. The class of foundations to be discussed in this chapce*. 
could appropriately be called Foundations for Bridge Piers, since 
the latter are about the only ones that are laid under water. In this 
class of work two difficulties have to be overcome, both of which 
require great resources and care on the part of the engineer. The 
first is found in the means to be used in preparing the bed of the 
foundation, and the second in preserving it from the scouring action 
of the water. 

Preventing the undermining of the foundation is generally not a 
matter of much difficulty. In quiet water or in a sluggish stream 
but little protection is required ; in which case it is sufficient to de¬ 
posit a mass of loose stone, or riprap, around the base of the pier. 
If there is danger of the riprap’s being undermined, the layer must 
be extended farther from the base, or be made so thick that, if 
undermined, the stone will fall into the cavity and prevent further 
damage. A willow mattress sunk by placing stones upon it is an 
economical and efficient means of protecting a structure against 
scour. A pier may be protected also by inclosing it with a row of 
piles and depositing loose rock between the pier and the piles. In 
minor structures the foundation may be protected by driving sheet 
piles around it. 

If a large quantity of stone be deposited around the base of the 
pier, the velocity of the current, and consequently its scouring 
action, will be increased. Such a deposit is also an obstruction to 
navigation, and therefore is seldom permitted. In many cases the 
only absolute security is in sinking the foundation below the scour¬ 
ing action of the water. The depth necessary to secure this adds to 
the difficulty of preparing the bed of the foundation. 

387. The principal difficulty in laying a foundation under water 
consists in excluding the water. If necessary, masonry can be laid 
under water by divers ; but this is very expensive and is rarely re¬ 
sorted to. 


257 


FOUNDATIONS UNDER WATER. 


[CHAP. XII. 


258 


There are five methods in use for laying foundations under water: 
(1) the method of excluding the water from the bed of the founda¬ 
tion by the use of a coffer-dam; (2) the method of founding the 
pier, without excluding the water, by means of a timber crib sur¬ 
mounted by a water-tight box in which the masonry is laid; (3) the 
method of sinking iron tubes or masonry wells to a solid substratum 
by excavating inside of them; (4) the method, in which the water is 
excluded by the presence of atmospheric air; and (5) the method of 
freezing a wall of earth around the site, inside of which the excava¬ 
tion can be made and the masonry laid. These several methods will 
be discussed separately in the order named. 


Art. 1. The Coffer-Dam Process. 

388. A coffer-dam is an inclosure from which the water is pumped 
and in which the masonry is laid in the open air. This method con¬ 
sists in constructing a coffer-dam around the site of the proposed 
foundation, pumping out the water, preparing the bed of the foun¬ 
dation by driving piles or otherwise, and laying the masonry on the 
inside of the coffer-dam. After the masonry is above the water the 
coffer-dam can be removed. 

389. Construction of the Dam.* The construction of coffer¬ 
dams varies greatly. In still, shallow water, a well-built bank of 
clay and gravel is sufficient. If there is a slow current, a wall of 
bags partly filled with clay and gravel does fairly well; a row of 
cement barrels filled with gravel and banked up on the outside has 
also been used. If the water is too deep for any of the above 
methods, a single or double row of sheet piles may be driven and 
banked up on the outside with a deposit of impervious soil sufficient 
to prevent leaking. If there is much of a current, the puddle on 
the outside will be washed away; or, if the water is deep, a large 
quantity of material will be required to form the puddle-wall; and 
hence the preceding methods are of limited application. 

390. The ordinary method of constructing a coffer-dam in deep 
water or in a strong current is shown in Fig. CO. The area to be 
inclosed is first surrounded by two rows of ordinary piles, m, m. On 
the outside of the main piles, a little below the top, are bolted two 


* See also § 317, page 214. 






ART. 1.] 


THE COEFER-DAM PROCESS. 


250 


longitudinal pieces, w, iv, called wales; and on the inside are fastened 
two similar pieces, g,g, which serve as guides for the sheet piles, s, s , 
while being driven. A rod, r, connects the top of the opposite 
main piles to prevent spreading when the puddle is put in. The 
timber, t, is put on primarily to carry the footway, f, and is some¬ 
times notched over, or otherwise fastened to, the pieces w, w to pre¬ 
vent the puddle space from spreading, b and b are braces extend¬ 
ing from one side of the coffer-dam to the other. These braces are 
put in position successively from the top as the water is pumped 



out; and as the masonry is built up, they are removed and the sides 
of the dam braced by short struts resting against the pier. 

The resistance to overturning is derived principally from the 
main piles, m, m. The distance apart and also the depth to which 
they should be driven depends upon the kind of bottom, the depth 
of water, and the danger from floating ice, logs, etc. Roles and 
formulas are here of but little use, judgment and experience being 
the only guides. The distance between the piles in a row is usually 
from 4 to 6 feet. 

The dimensions of the sheet piles (§ 329) employed will depend 
upon the depth and the number of longitudinal waling pieces used. 
Two thicknesses of ordinary 2-inch plank are generally employed. 
Sometimes for the deeper dams, the sheet piles are timbers 10 or 12 
inches square. 

The thickness of the dam will depend upon (1) the width of gang¬ 
way required for the workmen and machinery, (2) the thickness re- 







































































^60 


FOUNDATIONS UNDER WATER. 


[CHAP. XII. 


quired to prevent overturning, and (3) the thickness of puddle 
necessary to prevent leakage through the wall. The thickness of 
shallow dams will usually he determined by the first consideration ; 
but for deep dams the thickness will be governed by the second or 
third requirement. If the braces, b, b, are omitted, as is sometimes 
done for greater convenience in working in the colfer-dam, then the 
main piles, m, m, must be stronger and the dam wider in order to 
resist the lateral pressure of the water. A rule of thumb frequently 
used for this case is: “For depths of less than 10 feet make the 
width 10 feet, and for depths over 10 feet give an additional thick¬ 
ness of 1 foot for each additional 3 feet of wall.” Trautwine’s rule 
is to make the thickness of the puddle-wall three fourths of its 
height; but in no case is the wall to be less than 4 feet thick. If 
the coffer-dam is well braced across the inclosed area, the puddle- 
wall may vary from 3 feet for shallow depths to 10 feet for great 
depths; the former width has been successfully employed for depths 
of 18 to 20 feet, although it is considerably less than is customary. 

The puddle-wall should be constructed of impervious soil, of 
which gravelly clay is best. It is a common idea that clay alone, or 
olay and fine sand, is best. With pure clay, if a thread of water ever 
so small finds a passage under or through the puddle, it will steadily 
wear a larger opening. On the other hand, with gravelly clay, if 
the water should wash out the clay or fine sand, the larger particles 
will fall into the space and intercept first the coarser sand, and 
next the particles of loam which are drifting in the current of water; 
and thus the whole mass puddles itself better than the engineer 
/could do it with his own hands. An embankment of gravel is com¬ 
paratively safe, and becomes tighter every day. While a clay em¬ 
bankment may be tighter at first than a gravelly one, it is always 
liable to breakage. Before putting in the puddling, all soft mud 
and loose soil should be removed from between the rows of sheet 
piles. The puddling should be deposited in layers, and compacted 
as much as is possible without causing the sheet piles to bulge so 
much as to open the joints. 

391 . Coffer-dams are sometimes constructed by building a strong 
crib, and sinking it. The crib may be composed either of uprights 
framed into caps and sills and covered on the outside with tongued 
and grooved planks, or of squared timbers laid one on top of the 
other, log-house fashion, and well calked. The outer uprights are 



ART. 1.] 


THE COFEER-HAM PROCESS. 


261 


braced against the inside uprights and sills to prevent crushing 
inwards. This crib may be built on land, launched, towed to its 
final place, and sunk by piling stones on top or by throwing them 
into cells of the crib-work which are boarded up for that purpose. 
The bottom of the stream may be leveled off to receive the crib by 
dredging, or the dam may be made tight at the bottom by driving 
sheet piles around it. The crib must be securely bolted together 
(see § 381) vertically, or the buoyancy of the water will lift off the 
upper courses. 

A movable coffer-dam is sometimes constructed in the same 
general way, except that it is made in halves to allow of removal 
from around the finished pier. The two halves are joined together 
by fitting timbers between the projecting courses of the crib, and 
then passing long bolts vertically through the several courses. Some 
of the compartments are made water-tight to facilitate the move¬ 
ment of the crib from place to place.* 

Coffer-dams are also built by sinking an open crib, similar to the 
above, and then sheeting it on the outside by driving piles around 
it after it is sunk. For shallow depths, this method is very efficient. 

392 . Sometimes two coffer-dams are employed, one inside of the 
other, the outer one being used to keep out the water, and the inner 
one to keep the soft material from flowing into the excavation. The 
outer one may be constructed in any of the ways described above. 
The inner one is usually a frame-work sheeted with boards, or a crib 
of squared timbers built log-house fashion with tight joints. The 
inner crib is sunk (by weighting it with stone) as the excavation 
proceeds. The advantages of the use of the inner crib are (1) that 
the coffer-dam is smaller than if the saturated soil were allowed to 
take its natural slope from the inside of the dam to the bottom of 
the excavation ; (2) the space between the crib and the dam can be 
kept full of impervious material in case of any trouble with the out¬ 
side dam ; (3) the feet of the sheet piling are always covered, which 
lessens the danger of undermining or of an inflow of water and mud 
under the dam ; and (4) it also reduces to a minimum the material 
to be excavated. 

393 . Iron has been used in a few instances as a sheeting for cof¬ 
fer-dams. Plates are riveted together to form the walls, and stayed 

* For an illustrated example, see Proc. Engineer’s Club of Philadelphia, vol. iv. 
No. 4. 







26 2 


FOUNDATIONS UNDER WATER. 


[CHAP. XII.. 


on the inside by horizontal rings made of angle iron. Wood is 
cheaper and more easily wrought, and therefore generally preferred. 

394. Leakage. A serious objection to the use of coffer-dams is 
the difficulty of preventing leakage under the dam. One of the 
simplest devices to prevent this is to deposit a bank of gravel around 
the outside of the dam ; then if a vein of water escapes below the 
sheet piling, the weight of the gravel will crush down and fill the 
hole before it can enlarge itself enough to do serious damage. If the 
coffer-dam is made of crib-work, short sheet piles may be driven 
around the bottom of it; or hay, willows, etc., may be laid around 
the bottom edge, upon which puddle and stones are deposited ; or 
a broad flap of tarpaulin may be nailed to the lower edge of the 
crib and spread out loosely on the bottom, upon which stones and 
puddle are placed. A tarpaulin is frequently used when the 
bottom is very irregular,—in which case it would cost too much to 
level off the site of the dam ; and it is particularly useful where the 
bottom is rocky and the sheet piles can not be driven. 

When the bed of the river is rock, or rock covered with but a 
few feet of mud or loose soil, a coffer-dam only sufficiently tight to 
keep out the mud is constructed. The mud at the bottom of the 
inclosed area is then dredged out, and a bed of concrete deposited 
under the water (§ 154). Before the concrete has set, another coffer¬ 
dam is constructed, inside of the first one, the latter being made water¬ 
tight at the bottom by settling it into the concrete or by driving 
sheet piles into it. However, the better and more usual method is 
to sink the masonry upon the bed of concrete by the method de¬ 
scribed in Art. 2 (pages 266-71). 

It is nearly impossible to prevent considerable leakage, unless the 
bottom of the crib rests upon an impervious stratum or the sheet 
piles are driven into it. Water will find its way through nearly any 
depth or distance of gravelly or sandy bottom. Trying to pump a 
river dry through the sand at the bottom of a coffer-dam is expen¬ 
sive. However, the object is not to prevent all infiltration, but only 
to so reduce it that a moderate amount of bailing or pumping will 
keep the water out of the way. Probably a coffer-dam was never 
built that did not require considerable pumping; and not infre¬ 
quently the amount is very great,—so great, in fact, as to make it 
clear that some other method of constructing the foundation should 
have been chosen. 



ART. 1.] 


THE COFFER-DAM PROCESS. 


263 


Seams of sand are very troublesome. Logs or stones under the 
edge of the dam are also a cause of considerable annoyance. It is 
sometimes best to dredge away the mud and loose soil from the site 
of the proposed cotfer-dam ; but, when this is necessary, it is usu- 
ually better to construct the foundation without the use of a coffer¬ 
dam,—see Art. 2 of this chapter (page 266). Coffer-dams should 
be used only in very shallow water, or when the bottom is clay or 
some material impervious to water. 

395. Pumps. In constructing foundations, it is frequently neces¬ 
sary to do considerable bailing or pumping. The method to be em¬ 
ployed in any particular case will vary greatly with the amount of 
water present, the depth of the excavation, the appliances at hand, 
etc. The pumps generally used for this kind of work are (1) the ordi¬ 
nary wooden hand-pump, (2) the steam siphon, (3) the pulsometer, 
and ( 4 ) the centrifugal pump. Rotary and direct-acting steam 
pumps are not suitable for use in foundation work, owing to the 
deleterious effect of sand, etc., in the water to be pumped. 

1. Hand Power. When the lift is small, water can be bailed 
out faster than it can be pumped by hand ; but the labor is propor¬ 
tionally more fatiguing. The ordinary hand foundation-pump con¬ 
sists of a. straight tube at the bottom of which is fixed a common 
flap valve, and in which works a piston carrying another valve. The 
tube is either a square wooden box or a sheet-iron cylinder,—usually 
the latter, since it is lighter and more durable. The pump is oper¬ 
ated by applying the power directly to the upper end of the piston- 
rod, the pump being held in position by stays or ropes. There are 
more elaborate foundation-pumps on the market. 

2. The steam siphon is the simplest of all pumps, since it has 
no movable parts whatever. It consists essentially of a discharge 
pipe — 0 pen at both ends—through the side of which enters a smaller 
pipe having its end bent up. The lower end of the discharge pipe 
dips into the water ; and the small pipe connects with a steam boiler. 
The steam, in rushing out of the small pipe, carries with it the air 
in the upper end of the discharge pipe, thus tending to form a 
vacuum in the lower end of that pipe ; the water then rises in the 
discharge pipe and is carried out with the steam. Although it is 
possible by the use of large quantities of steam to raise small quan¬ 
tities of water to a great height, the steam siphon is limited prac¬ 
tically to lifting water only a few feet. Its cheapness and simplicity 



264 FOUNDATIONS UNDER WATER. [CHAP. XII 

are recommendations in its favor, and its efficiency is not much less 
than that of other forms of pumps. A common form of the steam 
siphon resembles, in external appearance, the Eads sand-pump 
represented in Fig. 66 (page 293). 

3 . The puhometer is an improved form of the steam siphon. It 
may properly be called a steam pump which dispenses with all mov¬ 
able parts except the valves. The height to which it may lift water 
is practically unlimited. 

4. The centrifugal pump* consists of a set of blades revolving in 
a short cylindrical case which connects at its center with a suction 
(or inlet) pipe, and at its circumference with a discharge pipe. The 
blades being made to revolve rapidly, the air in the case is carried 
outward by the centrifugal force, tending to produce a vacuum in 
the suction pipe ; the water then enters the case and is discharged 
likewise. The distance from the water to the pump is limited by 
the height to which the ordinary pressure of the air will raise the 
water ; f but the height to which a centrifugal pump can lift the' 
water is limited only by the velocity of the outer ends of the revolv¬ 
ing blades. When a quick application with a discharge of large 
quantities of water is the most important consideration, the cen¬ 
trifugal pump is of great value. Since there are no valves in action 
while the pump is at work, the centrifugal pump will allow sand 
and large gravel—in fact almost anything that can enter between 
the arms—to pass. Pumps having a 6-inch to 10-inch discharge 
pipe are the sizes most frequently used in foundation work. 

396. Preparing the Foundation. After the water is pumped 
out, the bed of the foundation may be prepared to receive the 
masonry by any of the processes described in §§ 283-91, which see. 
Ordinarily the only preparation is to throw out, usually with hand 
shovels, the soft material. The masonry may be started directly 
upon the hard substratum, or upon a timber grillage resting on 
the soil (§§ 309-10) or on piles (§ 380). 

397. Cost. It is universally admitted that estimates for the 
cost of foundations under water are very unreliable, and none are 
more so than those contemplating the use of a coffer-dam. The 
estimates of the most experienced engineers frequently differ greatly 


* Frequently, but improperly, called a rotai'y pump. 

t Some forms of centrifugal pumps must be immersed in the liquid to be raised. 





ART. 1.] 


THE COFFER-DAM PROCESS. 


265 


from the actual cost. The difficulties of the case have already been 
discussed (§ 394). 

For the cost of piles and driving, see §§ 346-54. The timber 
will cost, according to locality, anywhere from $15 to $25 per 
thousand feet, board measure. The cost of labor in placing the 
timber can not be given, since it varies greatly with the design, size,, 
depth, etc. The iron in drift-bolts, screw-bolts, and spikes, is 
usually estimated at 3^- to 5 cents per pound in place. Excavation 
in coffer-dams frequently costs as high as $1 to $1.50 per cubic 
yard, including the necessary pumping. 

398. Example. The following example is interesting as show¬ 
ing the cost under the most favorable conditions. The data are for 
© 

a railroad bridge across the Ohio River at Point Pleasant, W. Va.* 
There were three 250-foot spans, one 400-foot, and one 200-foot.. 
There were two piers on land and four in the water ; and all ex¬ 
tended about 90 feet above low water. The shore piers were 
founded on piles—driven in the bottom of a pit—and a grillage, con¬ 
crete being rammed in around the timber. The foundations under 
water were laid by the use of a double coffer-dam (§ 392). The 
water was 10 feet deep ; and the soil was 3 to 6 feet of sand and 
gravel resting on dry, compact clay. The foundations consisted of 
a layer of concrete 1 foot thick on the clay, and two courses of 
timbers. The quantities of materials in the six foundations, and 
the total cost, are as follows : 


Pine timber in cribs inside of coffer-dams, and in foundations, 273,210 ft. B.M.. 

Oak timber in coffer-dams, main and sheet piling. 244,412 “ “ 

Poplar timber in coffer-dams. 3,597 “ “ 

Round piles in foundation and coffer-dams. 13,571 lin. ft. 

Excavation in foundations. 4,342 cu. yds; 

Concrete “ “ . 649 

Riprap..... 997 

The total cost of foundations, including labor of all kinds, derricks, barges, 
engines, pumps, iron, tools, ropes, and everything necessary for the rapid com¬ 
pletion of the work was $64,652.62. 


In the construction of the bridge over the Missouri River, near 
Plattsmouth, Neb., a concrete foundation 49 feet long, 21 feet 
wide, and 32 feet deep, laid on shore, the excavation being through 
clay, bowlders, shale, and soapstone, to bed-rock (32 feet below 


* Engineering News , vol. xiii. p. 338. 













266 


FOUNDATION’S UNDER WATER. 


[CHAP. XII. 


surface of the water), cost $39,607.23, or $42.81 per yard for the 
concrete laid.* 

399. For the relative cost of foundations, see Art. 6, page 309. 

400. Conclusion. Uncertainty as to what trouble and expense a 
coffer-dam will develop usually causes engineers to choose some other 
method of laying the foundations for bridge piers. Coffer-dams 
are applicable in shallow depths only ; hence one objection to found¬ 
ing bridge piers by this process, particularly in rivers subject to 
scour or liable to ice gorges, is the danger of their being either un¬ 
dermined or pushed off the foundation. When founded in mud or 
sand, the first mode of failure is most to be feared. This danger is 
diminished by the use of piles or large quantities of riprap ; but 
such a foundation needs constant attention. When founded on 
rock, there is a possibility of the piers being pushed off the founda¬ 
tion ; for, since it is not probable that the coffer-dam can be pumped 
perfectly dry and the bottom cleaned before laying the masonry or 
depositing the concrete, there is no certainty that there is good 
union between the base of the pier and the bed-rock. 

Coffer-dams are frequently and advantageously employed in 
laying foundations in soft soils not under water, as described in 
§§316-21 (pages 214-15). 

Art. 2. The Crib and Open-Caisson Process. 

401. DEFINITIONS. Unfortunately there is an ambiguity in the 
use of the word caisson. Formerly it always meant a strong, water¬ 
tight box having vertical sides and a bottom of heavy timbers, in 
which the pier is built and which sinks, as the masonry is added, 
until its bottom rests upon the bed prepared for it. With the in¬ 
troduction of the compressed-air process, the term caisson was ap¬ 
plied to a strong, water-tight box—open at the bottom and closed 
at the top—upon which the pier is built, and which sinks to the 
bottom as the masonry is added. At present, the word caisson gen¬ 
erally has the latter meaning. In the pneumatic process, a water¬ 
tight box—open at the top—is usually constructed on the roof of 
the working chamber (“pneumatic chamber”), inside of which the 
masonry is built; this box also is called a caisson. The caisson 

* Exclusive of cost of buildings, tools, and engineering expenses. These items 
amounted to 6 per cent, of the total cost of the entire bridge. 






ART. 2.] THE CRIB AND OPEN-CAISSON PROCESS. 267 

open at the bottom is sometimes called an inverted caisson, and the 
one open at the top an erect caisson. The latter when built over 
an inverted, or pneumatic, caisson, is sometimes called a coffer-dam. 
For greater clearness the term caisson will be used for the inverted, 
or pneumatic, caisson ; and the erect caisson, which is built over a 
pneumatic caisson, will be called a coffer-dam. A caisson employed 
in other than pneumatic work will be called an open caisson. 

402. Principle. This method of constructing the foundation 
consists in building the pier in the interior of an open caisson, 
which sinks as the masonry is added and finally rests upon the bed 
prepared for it. The masonry usually extends only a foot or two 
below extreme low water, the lower part of the structure being com¬ 
posed of timber crib-work, called simply a crib. The open caisson is 
built on the top of the crib, which is practically only a thick bottom 
for the box. The timber is employed because of the greater facil¬ 
ity with which it may be put into place, as will appear presently. 
Timber, when always wet, is as durable as masonry ; and ordinarily 
there is not much difference in cost between timber and stone. 

If the soil at the bottom is soft and unreliable, or if there is 
danger of scour in case the crib were to rest directly upon the bot¬ 
tom, the bed is prepared by dredging away the mud (§ 407) to a 
sufficient depth or by driving piles which are afterwards sawed off 
(§ 378) to a horizontal plane. 

403. Construction of the Caisson. The construction of the 
caisson differs materially with its depth. The simplest form is 
made by erecting studding by toe-nailing or tenoning them into 
the top course of the crib and spiking planks on the outside. For 
a caisson 6 or 8 feet deep, which is about as deep as it is wise to 
try with this simple construction, it is sufficient to use studding 6 
inches wide, 3 inches thick, and 6 to 8 feet long, spaced 3 feet apart, 
mortised and tenoned into the deck course of the crib. The sides 
and floor (the upper course of the crib) should be thoroughly calked 
with oakum. The sides may be braced from the masonry as the 
sinking proceeds. When the crib is grounded and the masonry is 
above the water, the sides of the box or caisson are knocked off. 

When the depth of water is more than 8 to 10 feet, the caisson 
is constructed somewhat after the general method shown in Fig. 61. 
The sides are formed of timbers framed together and a covering of 
.thick planks on the outside. The joints are carefully calked to 



268 


FOUNDATIONS UNDER WATER. 


[CHAP. XE. 


make the caisson water-tight. In deep caissons, the sides can be 
built up as the masonry progresses, and thus not be in the way of 
the masons. The sides and bottom are held together only by the 
heavy vertical rods ; and after the caisson has come to a bearing 
upon the soil and after the masonry is above the water, the rods are. 
detached and the sides removed, the bottom only remaining as a 
part of the permanent structure. 

For an illustration of the form of caisson employed in sinking a 
foundation by the compressed-air process, see Plate I. 

404. The caisson should be so contrived that it can be. 




Fig. 61. 


grounded, and afterwards raised in case the bed is found not to 
be accurately leveled. To effect this, a small sliding gate is some¬ 
times placed in the side of the caisson for the purpose of filling it 
with water at pleasure. By means of this gate, the caisson can be 
filled and grounded; and by closing the gate and pumping out the 
water, it can be set afloat. The same result can be accomplished by 
putting on and taking off stone. 

Since the caisson is a heavy, unwieldy mass, it is not possible tc 
control the exact position in which it is sunk ; and hence it should 
be larger than the base of the proposed pier, to allow for a little ad¬ 
justment to bring the pier to the desired location. The margin to 






















































































ART. 2.] 


THE CRIB AND OPEN-CAISSON PROCESS. 


269 


be allowed will depend upon the depth of water, size of caisson, 
facilities, etc. A foot all round is probably none too much under 
favorable conditions, and generally a greater margin should bo 
allowed. 

405. Construction of the Crib. The crib is a timber struct¬ 
ure below the caisson, which transmits the pressure to the bed of 
the foundation. A crib is essentially a grillage (see § 309 and § 380) 
which, instead of being built in place, is first constructed and then 
sunk to its final resting place in a single mass. A crib is usually 
thicker, i. e ., deeper, than the grillage. If the pressure is great, the 
crib is built of successive courses of squared timbers in contact; but 
if the pressure is small, it is built more or less open. In either 
case, if the crib is to rest upon a soft bottom, a few of the lower 
courses are built open so that the higher portions of the bed may 
be squeezed into these cells, and thus allow the crib to come to an 
even bearing. If the crib is to rest upon an uneven rock bottom, 
the site is first leveled up by throwing in broken stone. If the bot¬ 
tom is rough or sloping, the lower courses of the crib are sometimes 
made to conform to the bottom as nearly as possible, as determined 
from soundings. This method requires care and judgment to pre¬ 
vent the crib from sliding off from the inclined bed, and should be 
used with great caution, if at all. 

The crib is usually built afloat. Owing to the buoyancy of the 
water, about one third of a crib made wholly of timber would pro¬ 
ject above the water, and would require an inconveniently large 
weight to sink it; therefore, it is best to incorporate considerable 
stone in the crib-work. If the crib is more or less open, this is 
done by putting a floor into some of the open spaces or pockets, 
which are then filled with stone. If the crib is to be solid, about 
every third timber is omitted and the space filled with broken stone. 

The timbers of each course should be securely drift-bolted (§ 381) 
to those of the course below to prevent the buoyancy of the upper 
portion from pulling the crib apart, and also to prevent any possi¬ 
bility of the upper part’s sliding on the lower. 

406. Timber in Foundations. The free use of timber in 
foundations is the chief difference between American and European 
methods of founding masonry in deep water. The consideration 
that led to its introduction in foundations was its cheapness. Many 
of the more important bridges built some years ago rest upon crib- 




270 FOUNDATIONS UNDER WATER. [CHAP. XII. 

work of round logs notched at their intersection and secured bv 
drift-bolts. At present, cribs are always built of squared timber. 
As a rule, there is now but very little difference between the cost 
of timber and masonry in foundations. The principal advantage 
in the use of the timber in foundations under water is the facility 
with which it is put into position. Soft wood or timber which 
in the air has comparatively little durability, is equally as good 
for this purpose as the hard woods. It has been conclusively proved 
that any kind of timber will last practically forever, if completely 
immersed in water. 

407 . Excavating the Site. When a pier is to be founded in 

a sluggish stream, it is only necessary to excavate a hole in the 
bed of the stream, in which the crib (or the bottom of the caisson) 
may rest. The excavation is usually made with a dredge, any form 
of which can be employed. The dipper dredge is the best, but the 
clam-shell or the endless chain and bucket dredge are sometimes 
used. If the bottom is sand, mud, or silt, the soil maybe removed 
(1) by pumping it with the water through an ordinary centrifugal 
pump (§ 395),—the suction hose of which is kept in contact with, 
or even a little below, the bottom,—or (2) by the Eads sand-pump 
(§ 448). With either of these methods of excavating, a simple frame 
or light coffer-dam may be sunk to keep part of the loose soil from 
running into the excavation. 

408 . If the stream is shallow, the current swift, and the bottom 
soft, the site may be excavated or scoured out by the river itself. 
To make the current scour, construct two temporary wing-dams, 
which diverge up stream from the site of the proposed pier. The 
wings can be made by driving stout stakes or small piles into the 
bed of the stream, and placing solid panels—made by nailing ordi¬ 
nary boards to light uprights—against the piles with their lower edge 
on the bottom. The wings concentrate the current at the location 
of the pier, increase its velocity, and cause it to scour out the bed of 
the stream. This process requires a little time, usually one to three 
days, but the cost of construction and operation is comparatively 
slight. 

When the water is too deep for the last method, it is sometimes 
possible to suspend the caisson a little above the bed of the stream, 
in which case the current will remove the sand and silt from under 
it. At the bridge over the Mississippi at Quincy, Ill., a hole 10 feet 



ART. 3.] 


DREDGING THROUGH WELLS. 


271 


deep was thus scoured out. If the water is already heavily charged 
with sediment, it may drop the sediment on striking the crib and 
thus fill up instead of scour out. Notwithstanding the hole is 
liable to be filled up by the gradual action of the current or by a 
sudden flood, before the crib has been placed in its final position, 
this method is frequently more expeditious and less expensive than 
using a coffer-dam. 

409. If .the crib should not rest squarely upon the bottom, it 
can sometimes be brought down with a water-jet (§ 343) in the 
hands of a diver. However, the engineer should not employ a 
diver unless absolutely necessary, as it is very expensive. 

410. If the soft soil extends to a considerable depth, or if the 
necessary spread of foundation can not be obtained without an un¬ 
desirable obstruction of the channel, or if the bottom is liable to- 
scour, then piles may be driven, upon which the crib or caisson may 
finally rest. Before the introduction of the compressed-air process, 
this was a very common method of founding bridge piers in our 
western rivers ; and it is still frequently employed for small piers. 
The method of driving and sawing off the piles has already been 
described—see Chapter XI. 

The mud over and around the heads of the piles may be sucked 
off with a pump, or it may be scoured out by the current (§ 408). 
The attempt is sometimes made to increase the bearing power of the 
foundation by filling in between the heads of the piles with broken 
stone or concrete; but this is not good practice, as the stone does 
but little good, is difficult to place, and is liable to get on top of the 
piles and prevent the crib from coming to a proper bearing. 

Art. 3. Dredging Through Wells. 

411. A timber crib is frequently sunk by excavating the material 
through apartments left for that purpose, thus undermining the 
crib and causing it to sink. Hollow iron cylinders, or wells of 
masonry with a strong curb, or ring, of timber or iron beneath them, 
are sunk in the same way. 

This method is applicable to foundations both on dry land and 
under water.* It is also sometimes employed in sinking shafts in 
tunneling and mining. 

412. Excavators. The soil is removed from under the crib 




272 


FOUNDATIONS UNDER WATER. 


[CHAP. XII. 


with a clam-shell dredge, or with an endless chain and bucket 
dredge, or with the Eads sand-pump, or, for small jobs, with the 
sand-pump employed in driving artesian wells. 

The clam-shell dredge consists of the two halves of a hemi¬ 
spherical shell, which rotate about a horizontal diameter ; the edges 
of the shell are forced into the soil by the Aveiglit of the machine 
itself, and the pull upon the chain to raise the excavator draws the 
two halves together, thus forming a hemispherical bucket which 
incloses the material to be excavated. The Morris and Cumming 
dredge consists of two quadrants of a short cylinder, hinged and 
operated similarly to the above. The Milroy dredge (represented at 
A in Fig. 62, page 274) appears to have the preference for this kind 
of work. It consists of a frame from which are suspended a num¬ 
ber of spherical triangular spades which are forced vertically into 
the ground by their own weight ; the pull upon the excavator to 
lift it out of the mud draws these triangles together and encloses 
the earth to be excavated. There are several forms of dredges 
similar to the above, but differing from them in details. 

For a description of the Eads sand-pump, see § 448. 

413. In one case in France, the soil was excavated by the aid of 
-compressed air. An 8-inch iron tube rested on the bottom, with its 
top projecting horizontally above the water ; and compressed air was 
discharged through a small pipe into the lower end of the 8-inch 
tube. The weight of the air and water in the tube was less than 
an equal height of the water outside ; and hence the water in the 
tube was projected from the top, and carried with it a portion of the 
mud, sand, etc. Pebbles and stones of considerable size were thus 
thrown out. See § 447. 

414. Noted Examples.— Poughkeepsie Bridge. The Pough¬ 
keepsie bridge, which crosses the Hudson at a point about 75 miles 
above New York City, is founded upon cribs, and is the boldest ex¬ 
ample of timber foundation on record. It is remarkable both for 
the size of the cribs and for the depth of the foundation. 

There are four river piers. The crib for the largest is 100 feet 
long, 60 feet wide at the bottom and 40 feet at the top, and 104 
feet high. It is divided, by one longitudinal and six transverse 
walls, into fourteen compartments through which the dredge worked. 
The side and division walls terminate at the bottom with a 12" x 
12" oak stick, which served as a cutting edge. The exterior walls 



ART. 3.] 


DREDGING THROUGH WELLS. 


273 


tind the longitudinal division wall were built solid, of triangular 
cross section, for 20 feet above the cutting edge, and above that 
they were hollow. The gravel used to sink the crib was deposited 
in these hollow walls. The longitudinal walls were securely tied to 
each other by the end and cross division walls, and each course of 
timber was fastened to the one below by 450 1-inch drift-bolts 30 
inches long. The timber was hemlock, 12 inches square. The 
fourteen compartments in which the clam-shell dredges worked 
were 10 X 12 feet in the clear. The cribs were kept level while 
sinking by excavating from first one and then the other of the com¬ 
partments. Gravel was added to the pockets as the crib sunk. 
When hard bottom was reached, the dredging pockets were filled 
with concrete deposited under water from boxes holding one cubic 
yard each and opened at the bottom by a latch and trip-line. 

After the crib was in position, the masonry was started in a 
floating caisson which finally rested upon the top of the crib. 
Sinking the crib and caisson separately is a departure from the 
ordinary method. Instead of using a floating caisson, it is generally 
considered better to construct a coffer-dam on top of the crib, in 
which to start the masonry. If the crib is sunk first, the stones 
which are thrown into the pockets to sink it are liable to be left 
projecting above the top of the crib and thus prevent the caisson 
from coming to a full and fair bearing. 

The largest crib was sunk through about 53 feet of w'ater, 20 
feet of mud, 45 feet of clay and sand, and 17 feet of sand and 
gravel. It rests, at 134 feet below high water, upon a bed of gravel 
16 feet thick overlying bed-rock. The timber work is 110 feet high, 
including the floor of the caisson, and extends to 14 feet below high 
water (7 feet below low water), at which point the masonry com¬ 
mences and rises 39 feet. On top of the masonry a steel tower 100 
feet high is erected. The masonry in plan is 25 X 87 feet, and has 
nearly vertical faces. The lower chord of the channel span is 130 
feet and the rail is 212 feet above high water. 

The other piers are nearly as large as the one here described. 
The cribs each contain an average of 2,500,000 feet, board measure, 
of timber and 350 tons of wrought iron. 

415. Atchafalaya Bridge. This bridge is over the Atchafalaya 
bayou or river, at Morgan City, La., about 80 miles west of New 
Orleans. The soil is alluvial to an unknown depth, and is subject 




274 


FOUNDATIONS UNDER WATER. 


[CHAP. XII. 


to rapid and extensive scour ; and no stone suitable for piers could 
be found within reasonable distance. Hence iron cylinders were 
adopted. They are foundation and pier combined. The cylinders 
were sunk 120 feet below high water—from 70 to 115 feet below the 
mud line—by dredging the material from the inside with a Milroy 
excavator. Fig. 62 shows the excavator and the appliances for 
handling the cylinders. 



The cylinders are 8 feet in outside diameter. Below the level 
, of the river bed, they are made of cast iron 1^ inches thick, in 
lengths of 10^ feet; the sections were bolted together through in¬ 
side flanges with 1-inch bolts spaced 5 inches apart. Above the 
river bottom, the cylinders are made of wrought-iron plates f inches 
thick, riveted together to form short cylindrical sections with angle- 
iron flanges. The bolts and spacing to unite the sections are the 
same as in the cast-iron portions. 

The cylinders were filled with concrete and capped with a heavy 



































































ART. 3.] 


DREDGING THROUGH WELLS. 


275 


cast-iron plate. Two such cylinders, braced together, form the pier 
between two 250-feet spans of a railroad bridge. 

The only objection to such piers relates to their stability. These 
have stood satisfactorily since 1883. 

416. Hawkesbury Bridge. The bridge over the Ilawkesbury 
River in south-eastern Australia is remarkable for the depth of the 
foundation. It is founded upon elliptical iron caissons 48 X 20 feet 
at the cutting edge, which rest upon a bed of hard gravel 12G feet 
below the river bed, 185 feet below high water, and 227 feet below 
the track on the bridge. The soil penetrated was mud and sand. 
The caissons were sunk by dredging through three tubes, 8 feet in 
diameter, terminating in bell-mouthed extensions, which met the 
cutting edge. The spaces between the dredging' tubes and the 
outer shell were filled with gravel as the sinking progressed. The 
caissons were filled to low water with concrete, and above, with cut- 
stone masonry. 

417. Brick Cylinders. In Germany a brick cylinder was sunk 
256 feet for a coal shaft. A cylinder 25J feet in diameter was sunk 
76 feet through sand and gravel, when the frictional resistance 
became so great that it could be sunk no further. An interior 
cylinder, 15 feet in diameter, was then started in the bottom of the 
larger one, and sunk 180 feet further through running quicksand. 
The soil was removed without exhausting the water. 

A brick cylinder—outer diameter 46 feet, thickness of wall 3 
feet—was sunk 40 feet in dry sand and gravel without any difficulty. 
It was built 18 feet high (on a wooden curb 21 inches thick), and 
weighed 300 tons before the sinking was begun. The interior earth 
was excavated slowly, so that the sinking was about 1 foot per day, 
—the walls being built up as it sank. 

In Europe and India masonry bridge piers are sometimes sunk 
by this process, a sufficient number of vertical openings being left 
through which the material is brought up. It is generally a tedious 
and slow operation. To lessen the friction a ring of masonry is some* 
times built inside of a thin iron shell. The last was the method em¬ 
ployed in putting down the foundations for the new Tay bridge.* 

418. Frictional Resistance. The friction between cylinders 
and the soil depends upon the nature of the soil, the depth sunk, 
and the method used in sinking. If the cylinder is sunk by either 


* For an illustrated account, see Engineering News, vol. xiv. pp. G6-6S. 







276 


FOUNDATIONS UNDER WATER. 


[CHAP. XI3. 


of the pneumatic processes (§§ 425 and 426), the flow of the water 
or the air along the sides of the tube greatly diminishes the fric¬ 
tion. It is impossible to give any very definite data. 

The following table * gives the values of the co-efficient of fric¬ 
tion f for materials and surfaces which occur in sinking foundations 
for bridge piers. Each result is the average of at least ten experi¬ 
ments. “All materials were rounded off at their face to sledge 
shape and drawn lengthwise and horizontally over the gravel or 
sand, the latter being leveled and bedded as solid as it is likely 
to be in its natural position. The riveted sheet iron contained 
twenty-five rivets on a surface of 2.53 X 1.67 = 4.22 square feet; 
the rivet-heads were half-round and -[f inch in diameter/’ Notice 
that for dry materials and also for wet gravel and sand, the frictional 
resistance at starting is smaller than during motion, which is con¬ 
trary to the ordinary statement of the laws of friction. 

TABLE 30. 

\ 

Co-efficient of Friction of Materials and Surfaces used in Foun¬ 
dations. 


Kind of Materials. 

For Dry 
Materials. 

For Wet 
Materials. 

At Begin¬ 
ning of 
Motion. 

During 

Motion. 

At Begin¬ 
ning of 
Motion. 

During 

Motion. 

Sheet iron without rivets on gravel and sand. 

0.40 

0.46 

0.33 

0.44 

“ “ with “ “ “ “ “ . 

0.40 

0.49 

0.47 

0.55 

Cast iron (unplaned) on gravel and sand. 

0.37 

0.47 

0.36 

0.50 

Granite (roughly worked) on gravel and sand.... 

0.43 

0.54 

0.41 

0.48 

Pine (sawed) on gravel and sand. 

0.41 

0.51 

0.41 

0.50 

Sheet iron without rivets on sand. 

0.54 

0.63 

0.37 

0.32 

“ “ with “ “ “ . 

0.73 

0.84 

0.52 

0.50 

Cast iron (unplaned) on sand. 

0.56 

0.61 

0.47 

0.38 

Granite (roughly worked) on sand. 

0.65 

0.70 

0.47 

0.53 

Pine (sawed) on sand. 

0.66 

0.73 

0.58 

0.48 


419. Values from Actual Practice. Cast Iron. During the 
construction of the bridge over the Seine at Orival, a cast-iron 


* By A. Schmoll in “ Zeitschrift des Yereines Deutscher Ingenieure,” as repub¬ 
lished in Selected Abstracts of Inst, of C. E., vol. lii. pp. 298-302. 

t The co-efficient of friction is equal to the total friction divided by the total 
normal pressure; that is to say, it is the friction per unit of pressure perpendicular 
to the surfaces in contact. 































ART. 3.] 


DREDGING THROUGH WELLS. 


m 


cylinder, standing in an extensive and rather uniform bed of gravel, 
•and having ceased to move for thirty-two hours, gave a frictional re~ 
sistance of nearly 200 lbs. per sq. ft.* At a bridge over the Danube 
near Stadlau, a cylinder sunk 18.75 feet into the soil (the lower 3.75 
feet being “ solid clay”) gave a frictional resistance of 100 lbs. per 
sq. ft.* * § According to some European experiments, the friction of 
cast-iron cylinders in sand and river mud was from 400 to 600 lbs. 
per sq. ft. for small depths, and 800 to 1,000 for depths from 20 to 
30 feet, f At the first Harlem River bridge. New York City, the 
frictional resistance of a cast-iron pile, while the soil around it was 
•still loose, was 528 lbs. per. sq. ft. of surface ; and later 716 lbs. per sq. 
ft. did not move it. From these two experiments, McAlpine, the en¬ 
gineer in charge, concluded that “1,000 lbs. per sq. ft. is a safe value 
for moderately fine material.” J At the Omaha bridge, a cast-iron 
pile sunk 27 feet in sand, with 15 feet of sand on the inside, could not 
be withdrawn with a pressure equivalent to 254 lbs. per sq. ft. of 
surface in contact with the soil ; and after removal of the sand from 
the inside, it moved with 200 lbs. per sq. ft. § 

Wrought Iron. A wrought-iron pile, penetrating 19 feet into 
■coarse sand at the bottom of a river, gave 280 lbs. per sq. ft.; an¬ 
other, in gravel, gave 300 to 335 lbs. per sq. ft.|| 

Masonry. In the silt on the Clyde, the friction oh brick and 
-concrete cylinders was about 3-J- tons per sq. ft.T The friction on 
the brick piers of the Dufferin (India) Bridge, through clay, was 
900 lbs. per sq. ft.** 

Pneumatic Caissons. For data on the frictional resistance of 
pneumatic caissons, see § 455. 

Piles. For data on the frictional resistance of ordinary piles, 
see §§ 370-71. 

420. Cost. It is difficult to obtain data under this head, 
since but comparatively few foundations have been put down 
by this process. Furthermore, since the cost varies so much with 

* Van Nostrand’s Engin’g Mag., vol. xx. pp. 121-22. 

t Proc. Inst, of C. E., vol. 1. p. 131. 

X McAlpine in Jour. Frank. Inst., vol. lv. p. 105; also Proc. Inst, of C. E., voi 
.xxvii. p. 286. 

§ Van Nostrand’s Engin’g Mag., vol. viii. p. 471. 

1 Proc. Inst, of C. E., vol. xv. p. 290. 

If Ibid., vol. xxxiv. p. 35. 

** Engineering News, vol. xix. p. 160. 







278 


FOUNDATIONS UNDER WATER. 


[CHAP. XII. 


the depth of water, strength of current, kind of bottom, danger of 
floods, requirements of navigation, etc., etc., no such data are valu¬ 
able unless accompanied by endless details. 

Cribs. The materials in the cribs will cost, in place, about as 
follows : timber from $30 to $40 per thousand feet, board measure • 
drift and screw bolts from 3J to 5 cents per pound ; concrete from 
$4 to $G per cubic yard. Under ordinarily favorable conditions, the 
sinking by dredging will cost about $1 per cubic yard. 

Iron Tubes. Wrought-iron plate work will cost, exclusive of 
freight, from 3 to 4J cents per pound ; cast-iron tubes, exclusive of 
freight, 1^ to 2 cents per pound. 

421. For the relative cost of different methods, see Art. 6 
of this chapter. 

422. Conclusion. A serious objection to this method of sink¬ 
ing foundations is the possibility of meeting wrecks, logs, or other 
obstructions, in the underlying materials ; but unless the freezing 
process (see Art. 5 of this chapter) shall prove all that is claimed 
for it, the method by dredging through tubes or wells is the only 
one that can be applied to depths which much exceed 100 feet—the 
limit of the pneumatic process. 

\ 

Art. 4. Pneumatic Process. 

424. The principle involved is the utilization of the difference 
between the pressure of the air inside and outside of an air-tight 
chamber. The air-tight chamber may be either an iron cylinder, 
which becomes at once foundation and pier, or a box—open below 
and air-tight elsewhere—upon the top of which the masonry pier 
rests. The former is called a pneumatic pile ; the latter a pneu¬ 
matic caisson. The pneumatic pile is seldom used now. There 
are two processes of utilizing this difference of pressure,—the 
vacuum and the plenum. 

425. Vacuum Process. The vacuum process consists in ex¬ 
hausting the air from a cylinder, and using the pressure of the at¬ 
mosphere upon the top of the cylinder to force it down. Exhausting 
the air allows the water to flow past the lower edge into the air- 
chamber, thus loosening the soil and causing the cylinder to sink. 
By letting the air in, the water subsides, after which the exhaustion 
may be repeated and the pile sunk still farther. The vacuum 





ART. 4.] 


PNEUMATIC PROCESS. 


279 


should be obtained suddenly, so that the pressure of the atmosphere 
shall have the effect of a blow; hence, the pile is connected by a 
large flexible tube with a large air-chamber—usually mounted upon 
a boat,—from which the air is exhausted. When communication is 
opened between the pile and the receiver, the air rushes from the 
former into the latter to establish equilibrium, and the external 
pressure causes the pile to sink. 

To increase the rapidity of sinking, the cylinders may be forced 
down by a lever or by an extra load applied for that purpose. In 
-case the resistance to sinking is very great, the material may be re¬ 
moved from the inside by a sand-pump (§ 448), or a Milroy or clam¬ 
shell dredge (§ 412) ; but ordinarily no earth is removed from the 
inside. Cylinders have been sunk by this method 5 or 6 feet by a 
single exhaustion, and 34 feet in 6 hours. 

The vacuum process has been superseded by the plenum process. 

426. Plenum, or Compressed-air, Process. The plenum, or 
compressed-air, process consists in pumping air into the air-chamber, 
so as to exclude the water, and forcing the pile or caisson down by 
a load placed upon it. An air-lock (§ 431) is so arranged that the 
workmen can pass into the caisson to remove the soil, logs, and 
bowlders, and to watch the progress of the sinking, without re¬ 
leasing the pressure. The vacuum process is applicable only in mud 
or sand; but the compressed-air process can be applied in all kinds 
of soil. 

427. History of Pneumatic Processes. It is said that Papin, 
the eminent physicist—born at Blois in 1647,—conceived the idea 
of employing a continued supply of compressed air to enable work¬ 
men to build under a large diving-bell. In 1779, Coulomb pre¬ 
sented to the Paris Academy of Science a paper detailing a plan for 
executing all sorts of operations under water by the use of com¬ 
pressed air. His proposed apparatus was somewhat like that now 
in general use. 

In England in 1831, Earl Dundonald, then Lord Cochrane, took 
out a patent for a device for sinking tubular shafts through earth 
and water, by means of compressed air. His air-lock was much like 
modern ones, and was to be placed at the top of the main shaft. 
His invention was made with a view to its use in tunneling under 
the Thames, and in similar enterprises. In 1841, Bush also took 
out a patent in England for a plan of sinking foundations by the 





280 


FOUNDATIONS UNDER WATER 


[CHAP. XII. 


aid of compressed air. A German, by name G. Pfaun Muller, made 
a somewhat similar design for a bridge at Mayence, in 1850 ; but as- 
his plan was not executed, it was, like the patents of Cochrane and 
Bush, little known till legal controversies in regard to patent-rights 
dragged them from obscurity. 

428. The first practical application of the plenum process was 
made in France in 1841 by M. Triger. In order to reach a vein of 
coal on a sandy island in the Loire, opposite to Chalons, he sunk 
an iron tube about 40 inches in diameter, some 60 feet, by the 
blows of heavy weights. The fine sand was removed from the in¬ 
terior by means of a scoop bucket. On reaching a layer of coarse 
gravel, he could not force the tube through. He therefore capped 
his tube with an air-lock, and by compressed air forced out the 
water which had all the while filled the tube, and sent workmen to 
the bottom. The pressure he used was never greater than two at¬ 
mospheres. The water was discharged through a small tube, into 
which, several feet from the bottom, a jet of air was allowed to 
enter, thus diminishing the specific gravity of the column till it 
was rapidly blown out. In 1845, Triger read a paper on the sinking 
of a tube.about 6 feet in diameter to a depth of 82 feet by the same 
method, and suggested the use of it for the construction of deep 
foundations for bridges. 

Dr. Potts, of England, generally has the credit of inventing the 
vacuum process, for which he took out a patent in 1848. Many 
times in sinking foundations by the vacuum process, the com¬ 
pressed-air process was resorted to so that men could enter the pile 
to remove obstructions; and finally the many advantages of the 
compressed-air process caused it to entirely supersede the vacuum 
process. At present the term “ pneumatic process ” is practically 
synonymous with compressed-air process. 

429. The first foundations sunk entirely by the compressed-air 
process were the pneumatic piles for the bridge at Rochester, Eng¬ 
land, put down in 1851. The depth reached was 61 feet. 

The first pneumatic caisson was employed at Kehl, on the east¬ 
ern border of France, for the foundations of a railroad bridge across 
the Rhine. 

430. The first three pneumatic pile foundations in America 
were constructed in South Carolina between 1856 and 1860. Im¬ 
mediately after the civil war, a number of pneumatic piles were 



ART. 4.] 


PNEUMATIC PROCESS. 


281 


sunk in western rivers for bridge piers. The first pneumatic cais¬ 
sons in America were those for the St. Louis bridge (§ 457), put 
down in 1870. At that time these were the largest caissons ever 
constructed, and the depth reached—109 feet 8J inches—has not 
yet been exceeded. 

Of late years, the pneumatic caisson has almost entirely super¬ 
seded the pneumatic pile ; in fact the plenum-pneumatic caisson 
has almost entirely superseded, except in very shallow water or in 
water over about 80 or 100 ft. deep, all other methods of founding 
bridge piers. 

431. Pneumatic Piles. Although pneumatic cylinders are now T 
rarely employed, they will be briefly described because of their 
historic interest. 

The cylinders are made of either wrought or cast iron. The 
wrought-iron cylinders are composed of plates, about half an inch 
thick, riveted together and strengthened by angle irons on the in¬ 
side, and re-inforced at the cuttting edge by plates on the outside 
both to increase the stiffness and to make the hole a little larger so 
as to diminish friction. The cast-iron cylinders are composed of 
sections, from 6 to 10 feet long and 2 to 8 feet in diameter, bolted 
together by inside flanges, the lower section being cast with a sharp 
edge to facilitate penetration. Two of these tubes, braced together, 
are employed for ordinary bridge piers ; and six small ones around 
a large one for a pivot pier. They are filled with concrete, with a 
few courses of masonry or a heavy iron cap at the top. 

Fig. 63 shows the arrangement of the essential parts of a pneu¬ 
matic pile. The apparatus as shown is arranged for sinking by the 
plenum process ; for the vacuum process the arrangement differs 
only in a few obvious particulars. The upper section constitutes 
the ciir-loch. The doors a and b both open downwards. To enter 
the cylinder, the wc: :men pass into the air-lock, and 'close the 
door a. Opening the e.ck d allows the compressed air to enter the 
lock ; and when the pressure is equal on both sides, the door b is 
opened and the workmen pass down the cylinder by means of a ladder. 
To save loss of air, the air-lock should be opened very seldom, or 
made very small if required to be opened often. 

The air-supply pipe connects with a reservoir of compressed air 
on a barge. If the air were pumped directly into the pile without 
the intervention of a storage reservoir, as was done in the early ap- 



282 


FOUNDATIONS UNDER WATER. 


[CHAP. XII. 


plications of tlie plenum process, even a momentary stoppage of the 
engine would endanger the lives of the workmen. 

432, The soil may be excavated by ordinary hand tools, elevated 
to the air-lock by a windlass and bucket, and passed out through 
the main air-lock. Sometimes a double air-lock with one large and 
3 ne small compartment is used, the former being opened only to let 
gangs of workmen pass and the latter to allow the passage of the 



skip, or bucket, containing the excavated material. Sometimes an 
auxiliary lock, g f, is employed. The doors /and g are so con¬ 
nected by parallel bars (not shown) that only one can be opened at 
i time. The excavated material is thrown into the chute, the 
door / is closed, which opens g , and the material discharges itself 
on the outside. 

Mud and sand are blown out with the sand-lift (§ 447) or sand- 
pump (§ 448) without the use of any air-lock. 

433. The cylinders are guided in their descent by a frame-work 
resting upon piles or upon two barges. One of the chief difficulties in 



























ART. 4.] 


PNEUMATIC PROCESS. 


2S3 


<~r. 


sinking pneumatic piles is to keep them vertical. If the cylinder 
becomes inclined, it can generally he righted (1) by placing wooden 
wedges under the lower side of the cutting edge, or (2) by excavat¬ 
ing under the upper side so that the air may escape and loosen the 
material on that side, or (3) by drilling holes through the upper¬ 
most side of the cylinder through which air may escape and loosen 
the soil, or (4) by straining the top over with props or tackle. If 
several pneumatic piles are to form a pier, they should be sunk one 
at a time, for when sunk at the same time they are liable to run 
together. 

434. Bearing Power. The frictional resistance of iron cylinders 
has been discussed in §§ 418-19, page 275-77, which see. 

McAlpine, in sinking the piers of the Harlem bridge, New York 
City, devised a very valuable but simple 
and cheap method of increasing the bear¬ 
ing power of a pneumatic cylinder (see 
Fig. 64). He attached to the lower end 
of the cylindrical column a hollow conical 
iron section, 
much 
The base 

creased by driving short sheet piles . .. ... ... .. 

obliquely under the lower edge of the :c • 

conical base and removing the soil from Fig. 64. 

under them, after which the whole was filled in with concrete.* 

In cold climates the contraction of the iron cylinder upon the 
masonry filling might rupture the former; hence, it is sometimes 
recommended to fill the pile below the frost line with asphaltic con¬ 
crete. It has also been proposed to line the cylinders with thick, 
soft wood staves, which will compress under the contraction of the 
iron cylinder. However, the danger from this cause is not very 
serious; for, after the concrete has set, it is strong enough to 
support the load if the iron case were removed. 

435. After the cylinder has reached the required depth, concrete 
enough to seal it is laid in compressed air; and when this has 
set, the remainder can be laid in the open air. A short distance 
at the top is usually filled with good masonry, and a heavy iron cap 
put over all. 



* Jour. Frank. Inst., vol. lv. pp. 98 and 177. 














284 


FOUNDATIONS UNDER WATER. 


[CHAP. XIR 


436. Pneumatic Caissons. A pneumatic caisson is an immense 
box—open below, but air-tight and water-tight elsewhere,—upon the 
top of which the masonry pier is built. The essential difference 
between the pneumatic pile and the pneumatic caisson is one of de¬ 
gree rather than one of quality. Sometimes the caisson envelops 
the entire masonry of the pier • but in the usual form the masonry 
envelops the iron cylinder and rests upon an enlargement of the 
lower end of it. The pneumatic pile is sunk to the final depth be¬ 
fore being filled with concrete or masonry; but with the caisson 
the masonry is built upward while the whole pier is being sunk 
downward, the masonry thus forming the load which forces the 
caisson into the soil. A pneumatic caisson is, practically, a gigantic 
diving bell upon the top of which the masonry of the pier rests. 

Fig. G5 is a section of a pier of the bridge across the Missouri 
River near Blair, Neb.,* and shows the general arrangement of the 
pier and pneumatic caisson. The tube extending through the mid¬ 
dle of the caisson and pier, known as the air-shaft, is for the ascent 
and descent of the men. The air-loch —situated at the junction of 
the two cylinders which form the air-shaft—consists of a short sec¬ 
tion of a large cylinder which envelops the ends of the tAVO sections 
of the air-shaft, both of which communicate with the air-lock by 
doors as shown in Fig. G5. The apartment in which the men are 
at work is known as the working chamber or air-chamber . The 
small cylinders shown on each side of the air-shaft are employed in 
supplying concrete for filling the working chamber when the sinking 
is completed. The pipes seen in the air-chamber and projecting 
above the masonry are employed in discharging the mud and sand, 
as will be described presently. The timbers which appear in the 
lower central portion of the working chamber are parts of the trusses 
which support the central portions of the roof of the caisson. 

The masonry is usually begun about 2 feet below low water, the 
space intermediate between the masonry and the roof of the working 
chamber being occupied by timber crib-work, either built solid or 
filled with concrete. In Fig. 65 the masonry rests directly upon 
the roof of the air-chamber, which construction was adopted for the 
channel piers of this bridge to reduce to a minimum the obstruction 
to the flow of the water. 

Frequently a coffer-dam is built upon the top of the crib (see 


* From the report of Geo. S. Morison, chief engineer of the bridge. 






ART. 4.] 


PNEUMATIC PROCESS 


285- 


Plate I); but in this particular case the masonry was kept above the 
surface of the water, hence no coffer-dam was employed. When 



Fig. 65 .—Pneumatic Caisson.—Blair Bridge. 


the coffer-dam is not used, it is necessary to regulate the rate of 
sinking by the speed with which the masonry can be built, which is 
liable to cause inconvenience and delay. When the coffer-dam is 



















































































FOUNDATIONS UNDER WATER. 


[CHAP. XII. 


286 


dispensed with, it is necessary to go on with the construction of the 
masonry whether or not the additional weight is needed in sinking 
the caisson. 

437. The details of the construction of pneumatic caissons can 
be explained best by the description of a particular case. 

438. Foundation of the Havre de Grace Bridge. Folding 
Plate I * shows the details of the construction of the caisson, crib, 
and coffer-dam employed in 1884 in sinking pier No. 8 of the 
Baltimore and Ohio R. R. bridge across the Susquehanna River at 
Havre de Grace, Md. The timber work of Fig. 66 (page 293) also 
shows some of the details of the construction of the walls of the 
working chamber. 

439. The Caisson. The details of the construction of the caisson 
areas follows: Six courses of timber, 12 X 12 inch, one lying on top 
of the other, formed the skeleton of the walls of the working cham¬ 
ber. These timbers were first put up with a batter of f of an inch 
horizontal to 1 foot vertical; they were not halved at the corners, 
but every alternate piece was carried through with a full section, 
“ log-house” fashion. These timbers were fastened at the corners, 
intersections, and several intermediate points, with drift-bolts (§ 381) 
1 inch square and 22 inches long. Inside of this timber shell, three 
courses of 3-inch plank, placed diagonally, were spiked to the hori¬ 
zontal timbers and to each other by 6-inch and 7-inch boat-spikes. 
Inside of the diagonal planking was another course of 3-inch plank 
placed vertically and well spiked, the head of each spike being 
wrapped with oakum to prevent leakage. The vertical seams were 
thoroughly calked. 

A strong and thoroughly braced truss (see also Fig. 66, page 293) 
was next erected longitudinally through the center of the working 
chamber. The first course in the deck of the working chamber was 
then placed in position on the central truss and side walls. The work¬ 
ing chamber was 9 feet 3 inches high from bottom of shoe to the 
underside of deck, which was higher than required for working, but 
was adopted so as to permit greater depth of the central truss. Out¬ 
side of the horizontal timbers, after they had been adzed to a true 
surface, were then placed the 12- by 14-inch sticks (shown at the ex- 

* Compiled from the original working drawings. The accompanying description 
is from personal inspection aided by an article in Engineering News by Col. Wm. M 
Patton, engineer in charge. 







ART. 4.] 


PNEUMATIC PROCESS. 


28? 


treme left of Fig. 66) 15 feet long, extending 2 feet below the bottom 
horizontal timber and having their lower ends beveled as shown. 
These timbers extended 6 feet above the horizontal members, 
and were shouldered at the upper end so that three of the deck 
courses rested upon them. Four screw-bolts were passed through 
each outside post and through the entire wall; and, in addition to 
these, two drift-bolts, 1 inch square and 30 inches long, in each ver¬ 
tical served to more thoroughly bind the wall together. This com¬ 
pound of timber and planking formed the walls of the working 
chamber. After the first deck course was in place, a few pieces of 
the second course were laid diagonally to give it stiffness; the under¬ 
side of this deck or roof was then lined with planks and thoroughly 
calked, and a false bottom put into the working chamber prepara¬ 
tory to launching it. 

After the caisson was launched the deck courses, eight in all, 
were put on. The first course was made of singledength timbers, 
reaching from inside to inside of the vertical wall posts, and resting 
on top of the horizontal timbers and inside planking and also on the 
top chord of the central truss, and being fastened to these members 
by 22-inch drift-bolts. The second course was laid diagonally and 
was made of varying lengths of timbers. The third course was laid 
from side to side across the caisson, and the fourth course longi¬ 
tudinally and resting on the shoulders of the 12 X 14 inch verticals. 
The fifth course was laid across, the sixth diagonally—crossing the 
second course,—and the seventh and eighth courses extended to the 
extreme outside limits of the caisson and rested on the heads of the 
vertical posts. This general arrangement of the top courses, resting 
as they did on the heads and shoulders of the outside verticals, gave 
a direct bearing on the posts and relieved the wall bolts of the great 
shearing strain to which they would otherwise have been subjected. 

The outside posts were bolted to the deck courses by one 3-foot 
screw-bolt and two 30-inch drift-bolts, fastening them to the longi¬ 
tudinal and diagonal courses respectively. The several deck courses 
were bolted to each other by 22-inch drift-bolts (not shown in the 
illustrations), spaced 5 feet apart along each stick. All the timbers 
in the deck were bedded in cement mortar and the vertical joints 
were grouted, so as to give a full and uniform bearing for each stick 
and also decrease the leakage and danger from fire. 

The center truss (see also Fig. 66) was constructed to bear a uni- 




288 


FOUNDATIONS UNDER WATER. 


[CHAP. XII. 


forrnly distributed load, or to act as a cantilever. It was composed 
•of a top and bottom chord, each made of two 12 x 12 inch sticks, 
with posts and diagonals of wood, and vertical and diagonal tie-rods 
1|- inch m diameter; the iron vertical rods extended through the 
first deck courses, and the top chord was also bolted to the deck 
with drift-bolts. The object of this was to enable the truss to act 
as a stiffening rib to the deck, independently of its action as a 
girder. The bottom chord was also extended to the ends, and by 
means of straps and bolts acted both as a strut and tie-brace for the 
ends of the caisson, and constituted the only end bracing. 

The sides of the caissons were braced against outside pressures by 
16 X 16 inch timbers abutting against the walls and bottom chord of 
the center truss, and against pressure from the inside by 2-inch iron 
tie-rods extending from out to out of the caisson, none of which are 
•shown. All the timber used, except the planking and outside posts 
und the bracing in the working chamber, was 12x12 inch. Iron 
straps, extending 6 feet on the sides and ends, were placed at the 
corners and bolted to the caisson timbers. These straps were made 
of bar-iron 3x1 inch and prevented spreading of the walls of the 
•caisson under excessive pressure within. Planks were spiked to the 
lower part of the posts ; and also a narrow plank, called a shoe, was 
spiked under the bottom of the posts (see Fig. 66). 

440. “ The construction was simple and strong ; in no case was 
there any bending or springing of the walls. The arrangement of 
the cutting edge with square shoulders was a departure from the 
ordinary V-shape (compare Figs. 65 and 66, pages 285 and 293), 
and was found to possess many advantages. It enabled the men to 
better regulate the sinking of the caisson by giving an increased bear¬ 
ing surface. With this support, the material could be cleaned out 
from under one side or end ; the caisson could be leveled ; and, if 
the material was softer in one spot than another, the caisson could 
be prevented from tipping. It further afforded a good surface for 
blocking up when it was found desirable to support the caisson 
during the removal of the material ; and it gave also greater security 
in case of a ‘blow-out 9 or the failure of air-pressure.” * 

When it is anticipated that gravel or bowlders will be met with 
in sinking, the cutting edge is usually shod with iron. The iron 
cutting edge was omitted in all the caissons for this bridge, and it is 

* Col. Wm. M. Patton, engineer in charge for the railroad companyT~ 





ART. 4.] 


PNEUMATIC PROCESS. 


289 


claimed that the experience here shows that “ in no case is an iron 
shoe either advantageous or necessary.” 

441. The Crib. The construction of the crib is shown very fully 
in Plate I. The timbers were all 12.X 12 inches square, bolted to 
each other by 22-inch drift-bolts—spaced 5 or 6 feet apart,—and 
were dovetailed at the corners and connections. The parts of all 
the walls of the crib were firmly bolted to the deck of the caisson. 

Ordinarily the division walls of the crib are built vertically from 
top to bottom ; but in this case, they were off-set, as shown, to 
secure a better bond in the mass of concrete* If the walls are built 
solid from top to bottom, the concrete filling is thereby divided into 
a number of separate monolithic columns; but in the construction 
as above, the concrete forms practically a single solid mass. The 
walls are built solid, owing to the difficulty of getting the concrete 
thoroughly packed in around so many timbers. Large stones, such 
as could be handled by one man, were bedded in mortar as the suc¬ 
cessive layers of concrete were formed, and over and around these 
another layer of concrete was rammed. In most localities there is 
but little difference in cost between a solid timber crib and one with 
timber pockets filled with concrete. 

442. The Coffer-dam. Uprights were first placed at intervals of 
about 5^ feet, and connected by mortise and tenon to caps and 
sills. This frame-work was held down to the crib by rods 2 inches 
in diameter, having hooks at the lower end which passed into eye- 
bolts in the sides of the crib. On the sides of the dam, the upper 
end of these rods passed through 12 X 12 inch timbers resting on 
the sides of the dam and projecting about 2 feet outside; and at the 
ends of the dam, they passed through short pieces bolted to one of 
the cross timbers and projecting beyond the end of the dam. 

Owing to the great depth required, the coffer-dam was built in 
sections, the connecting rods being made in sections with swivel 
connections. The second section was not added until the depth 
sunk required it. When the top section of the dam was put on, 
the projecting ends of the timbers through which the connecting 
rods passed were sawed off. The bottom section was sheeted with 
three courses of 3-inch plank, and the top section with two thick¬ 
nesses. The joint between the coffer-dam and the crib, and also 
‘he sheeting, were well calked. 

The sides of the coffer-dam were braced against the pressure of 



290 


FOUNDATIONS UNDER WATER. 


[CHAP. XII. 


the water, by 12 X 12 inch timbers resting on the top of each sec- 
tion, and by a system of bracing in the middle of each section. 
When the masonry was completed, the coffer-dam was removed by 
disconnecting the vertical rods. 

443. Machinery Barge. The machinery barge was an ordinary 
flat-boat fitted up for the purpose. At one end of the barge there 
were three boilers each of fifty horse-power. In the middle were 
two large air-compressors, designed by the contracting engineer, 
Gen. Wm. Sooy Smith. One furnished all the compressed air re¬ 
quired, the other being ready for use in case of any accident or 
break-down. At the other end of the boat were two Worthington 
steam pumps to furnish water for the excavating plant used in the 
caisson. There were also a small engine and a dynamo which fur¬ 
nished the current for the electric lamps used in the caisson and, at 
night, on the outside. 

444. Material Required. Table 31 gives the dimensions and 
quantities of materials in the pneumatic foundations of this bridge, 
and Table 32 (page 302) gives the cost. 

TABLE 31. 

Dimensions and Quantities of Materials in Foundations of 

Havre de Grace Bridge.* 


Description. 

Number of the Pier. 

II. 

HI. 

IV. 

vm. 

IX. 

Dimensions: 






Caissons: — length at bottom, in feet. 

63.3 

67.3 

79.4 

70.9 

78.2 

width “ “ “ “ . 

25.9 

25.9 

32.8 

32.6 

42.3 

height from cutting edge, iu feet.. 

17.2 

17.2 

17.2 

17.2 

19.3 

height of working chamber, in feet 

9.2 

9.2 

9.2 

9.2 

9.2 

Crib:—length, in feet. 

61.5 

61.5 

77.6 

69.1 

76.4 

width, “ “ . 

24.2 

24.2 

31.1 

30.8 

40.5 

height, “ “ . 

40.0 

42.0 

22.2 

41.0 

32.8 

Quantities: 






Timber in the caisson, feet, board measure. 

203.473 

215.565 

316,689 

281,540 

465,125 

“ “ “ crib, 

179,939 

197,910 

143.993 

219,680 

203,824 

“ “ “ coffer-dam. 41 

2.068 

31,517 

108,518 

85,759 

126,532 

Concrete in working chamber, cubic yards... 

330 

401 

631 

559 

'839 

“ crib, shafts, etc., “ “ ... 

1,649 

1,893 

1,635 

2,581 

3,172 

below cutting edge, “ “ ... 

000 

623 

126 

526 

624 

Iron, screw-bolts, pounds. 

11.313 

15,651 

32,881 

31.026 

33,435 

drift-bolts, “ . 

34,181 

36,832 

40,909 

44,861 

59,245 

spikes, “ . 

4,638 

700 

11.730 

10.039 

11,237 

cast washers, “ . 

2,472 

2,572 

3,392 

3,235 

3,535 


* The data by courtesy of Sooysmith & Co., contractors for the pneumatic foundations. 

445. Position of the Air-lock. Before the construction of 
the St. Louis bridge, the air-lock had always been placed at the top 




























ART. 4.] 


PNEUMATIC PROCESS. 


291 


of the air-shaft, and was of such construction that to lengthen the 
shaft, as the caisson sunk, it was necessary to detach the lock, add 
a section to the shaft, and then replace the lock on top. This was 
not only inconvenient and an interruption to the other work, but 
required the men to climb the entire distance under compressed 
air, which is exceedingly fatiguing (see § 460). To overcome these 
objections, Eads placed the air-lock at the bottom of the shaft. 
This position is objectionable, since in case of a “ blow-out,” e. r 
a rapid leakage of air,—not an unfrequent occurrence,—the men 
may not be able to get into the lock in time to escape drowning. If 
the lock is at the top, they can get out of the way of the water by 
climbing up in the shaft. 

At the Havre de Grace bridge, the air-shaft was constructed of 
wrought iron, in sections 15 feet long. The air-lock was made by 
placing diaphragms on the inside flanges of the opposite ends of the 
top section. A new section and a third diaphragm could be added 
without disturbing the air-lock; and when the third diaphragm 
was in place, the lower one was removed preparatory to using it 
again. Some engineers compromise between these two positions, 
and leave the air-lock permanently at some intermediate point in 
the pier (see Fig. 65, page 285). 

446. Excavators. In the early application of the pneumatic 
method, the material was excavated with shovel and pick, elevated 
in buckets or bags by a windlass, and stored in the air-lock. When 
the air-lock was full, the lower door was closed, and the air in the 
lock was allowed to escape until the upper door could be opened, 
and then the material was thrown out. This method was expensive 
and slow. 

In the first application of the pneumatic process in America 
(§ 430), Gen. Wm. Sooy Smith invented the auxiliary air-lock , g f, 
Fig. 63 (page 282), through which to let out the excavated mate¬ 
rial. The doors, / and g, are so connected together that only one 
of them can be opened at a time. The excavated material being 
thrown into the chute, the closing of the door / opens g, and the 
material slides out. This simple device is said to have increased 
threefold the amount of work that could be done. 

447. Sand-lift. This is a device, first used by Gen. Wm. Sooy 
Smith, for forcing the sand and mud out of the caisson by means 
of the pressure in the working chamber. It consists of a pipe. 






292 


FOUNDATIONS UNDER WATER. 


[CHAP. XII. 


reaching from the ivorking chamber to the surface (see Fig. 63 and 
Plate I), controlled by a valve in the working chamber. The sand 
is heaped up around the lower end of the pipe, the valve opened, 
and the pressure forces a continuous stream of air, sand, and water 
up and out. For another application of this principle, see § 413. 

In sand, this method of excavating is very efficient, being eight 
to ten times as expeditious as the auxiliary air-lock. Of course, 
the efficiency varies with the depth, i. e., with the pressure. When 
the soil is so impervious that the water in the working chamber can 
not be forced out under the edge of the caisson, it is made to pass 
through the sand-lift pipe. 

The “goose-neck,” or elbow at the top of the discharge pipe, is 
worn away very rapidly by the impact of the ascending sand and 
pebbles. At the Havre de Grace bridge, it was of chilled iron 4 
inches thick on the convex side of the curve, and even then lasted 
only two days. At the Brooklyn bridge, the discharge pipe ter¬ 
minated with a straight top, and the sand was discharged against a 
block of granite placed in an inclined position over the upper end. 

Although the sand-lift is efficient, there are some objections to 
it: (1) forcing the sand out by the pressure in the cylinder de¬ 
creases the pressure, which causes, particularly in pneumatic piles or 
small caissons, the formation of vapors so thick as to prevent the 
workmen from seeing; (2) the diminished pressure allows the 
water to flow in under the cutting edge ; and (3) if there is much 
leakage, the air-compressors are unable to supply the air fast 
enough. 

448. Mud-pump. During the construction of the St. Louis 
bridge, Capt. Eads invented a mud-pump, which is free from the 
above objections to the sand-lift, and which in mud or silt is more 
efficient than it. This device is generally called a sand-pump, but 
ig more properly a mud-pump. 

The principle involved in the Eads pump is the same as that 
employed in the atomizer, the inspirator, and the injector; viz., the 
principle of the induced current. This principle is utilized by dis¬ 
charging a stream of water with a high velocity on the outside of a 
small pipe, which produces a partial vacuum in the latter; when 
the pressure of the air on the outside forces the mud through the 
small pipe and into the current of water by which the mud is 
carried away. The current of water is the motive power. 




ART. 4.] 


PNEUMATIC PROCESS. 


293 


Fig. 66 is an interior view of the caisson of the Baltimore and 
Ohio R. R. bridge at Havre de Grace, Md., and shows the general 
arrangement of the pipes and mud-pump. The pump itself is a 




























































































294 


FOUNDATIONS UNDER WATER. 


[CHAP. XII.. 


hollow pear-shaped casting, about 15 inches in diameter and 15* 
inches long, a section of which is shown in the corner of Fig. 66. 
The water is forced into the pump at a, impinges against the coni¬ 
cal casing, d , flows around this lining and escapes upwards through 
a narrow annular space, /. The interior casing gives the water an 
even distribution around the end of the suction pipe. The flow of 
the water through the pump can be regulated by screwing the suc¬ 
tion pipe in or out, thus closing or opening the annular space, f. 
To prevent the too rapid feeding or the entrance of lumps, which 
might choke the pipe, a strainer—simply a short piece of pipe, 
plugged at the end, having a series of J-inch to f-inch holes bored 
in it—was put on the bottom of the suction pipe. The discharge 
pipe of the mud-pump terminates in a “ goose-neck 99 through 
which the material is discharged horizontally. 

The darkly shaded portions of the section of the pump wear 
away rapidly ; and hence they are made of the hardest steel and 
constructed so as to be readily removed. Different engineers have 
different methods of providing for the renewal of these parts, the 
outline form of the pump varying with the method employed. The 
pump used at the St. Louis bridge was cylindrical in outline, but 
otherwise essentially the same as the above. 

449. In order to use the mud-pump, the material to be exca¬ 
vated is first mixed into a thin paste by playing upon it with a jet 
of water. This pump is used only for removing mud, silt, and soil 
containing small quantities of sand ; pure sand or soil containing 
large quantities of sand is “ blown out ” with the sand-lift. 

The water is delivered to the mud-pump under a pressure, ordi¬ 
narily, of 80 or 90 pounds to the square inch. At the St. Louis 
bridge, it was found that a mud-pump of 3-J-inch bore was capable 
of raising 20 cubic yards of material 120 feet per hour, the water 
pressure being 150 pounds per square inch.* 

450. Water-column. A combination of the pneumatic process 
and that of dredging in the open air through tubes has been em¬ 
ployed extensively in Europe. It seems to have been used first at 
the bridge across the Rhine at Kehl. The same method was used 
at the Brooklyn bridge. The principle is rudely illustrated in 


* History of the St. Louis Bridge, p. 213. 






ART. 4.] 


PNEUMATIC PROCESS. 


295 


Fig. 07. The central shaft, which is open top and bottom, projects 
a little below the cutting edge, 
and is kept full of water, the 
greater height of water in the 
column balancing the pressure 
of the air in the chamber. The 
workmen simply push the mate¬ 
rial under the edge of a water- 
shaft, from whence it is exca¬ 
vated by a dredge (§ 412). 

451. Blasting. Bowlders or 
points of rock may be blasted in 
compressed air without any ap¬ 
preciable danger of a “ blow¬ 
out ” or -of injuring the ear¬ 
drums of the workmen. This 
point was settled in sinking the foundations of the Brooklyn bridge ; 
and since then blasting has been resorted to in many cases. Bowl¬ 
ders are sometimes “carried down,” i. e., allowed to remain on the 
surface of the soil in the working chamber as the excavation pro¬ 
ceeds, and subsequently imbedded in the concrete with which the 
air-chamber is filled. 

452. Rate of Sinking. The work in the caisson usually con¬ 
tinues da} 7 and night, winter and summer. The rate of progress 
varies, of course, with the kind of soil, and particularly with the 
number of bowlders encountered. At the Havre de Grace bridge, 
the average rate of progress was 1.37 ft. per day; at Plattsmouth, 
2.22 ft. ; and at Blair, 1.75 ft. per day. 

453. Guiding the Caisson. Formerly it was the custom to 
control the descent of the caisson by suspension screws connected 
with a frame-work resting upon piles or pontoons. In a strong 
current or in deep water, it may be necessary to support the caisson 
partially in order to govern its descent; but ordinarily the suspension 
is needed only until the caisson is well imbedded in the soil. The 
caisson may be protected from the current by constructing a break¬ 
water above and producing dead water at the pier site. 

After the soil has been reached, the caisson can be kept in its 
course by removing the soil from the cutting edge on one side or 
the other of the caisson. In case the caisson does not settle down 

































296 


FOUNDATIONS UNDER WATER. 


[CHAP. XII. 


after the soil has been removed from under the cutting edge, a re¬ 
duction of a few pounds in the air pressure in the working chamber 
is usually sufficient to produce the desired result. At the Havre de 
Grace bridge, it was found that by allowing the discharged mate¬ 
rial to pile up against the outside of the caisson, the latter could 
bemoved laterally almost at will. The top of the caisson was made 
3 feet larger, all round, than the lower course of masonry, to allow 
for deviation in sinking. The deviation of the caisson, which was 
founded 90 feet below the water, was less than 18 inches, even 
though neither suspension screws nor guide piles were employed. 

In sinking the foundations for the bridge over the Missouri 
River near Sibley, Mo., it was necessary to move the caisson con¬ 
siderably horizontally without sinking it much farther. This was 
accomplished by placing a number of posts—12 inches square— 
in an inclined position between the roof of the working chamber 
and a temporary timber platform resting on the ground below. 
When these posts had been wedged up to a firm bearing, the 
air pressure was released. The water flowing into the caisson 
loosened the soil on the outside, and the weight of the caisson com¬ 
ing on the inclined posts caused them to rotate about their lower 
ends, which forced the caisson in the desired direction. In this 
way, a lateral movement of 3 or 4 feet was secured while sinking 
about the same distance. 

A caisson is also sometimes moved laterally, wffiile sinking, 
by attaching a cable which is anchored off to one side and kept 
taut. 

454. A new method of controlling the descent of the caisson has 
been recently introduced, which is specially valuable in swift cur¬ 
rents or in rivers subject to sudden rises. It w T as used first in the 
construction of the piers for a bridge across the Yazoo River near 
Vicksburg, Miss. A group of 72 piles, each 40 feet long, was driven 
into the river bed, and sawed off under the water ; the caisson was 
then floated into place, and lowered until the heads of the piles 
rested against the roof of the working chamber. As the work 
proceeded, the piles were sawed off to allow the caisson to sink. 
One of the reasons for employing piles in this case, was that, if the 
caisson did not finally rest upon bed-rock, they would assist in sup¬ 
porting the pier. 

That such ponderous masses can be so certainly guided in their 



ART. 4.] 


PNEUMATIC PROCESS. 


297 


descent to bed-rock, is not the least valuable nor least interesting 
fact connected with this method of sinking foundations. 

455. Frictional Resistance. At the Havre de Grace bridge, 
the normal frictional resistance on the timber sides of the pneumatic 
caisson was 280 to 350 lbs. per sq. ft. for depths of 40 to 80 feet, 
the soil being silt, sand, and mud ; when bowlders were encoun¬ 
tered, the resistance was greater, and when the air escaped in large 
quantities the resistance was less. At the bridge over the Missouri 
River near Blair, Neb., the frictional resistance usually ranged be¬ 
tween 350 and 450 lbs. per sq. ft., the soil being mostly fine sand 
with some coarse sand and gravel and a little clay. At the Brook¬ 
lyn bridge the frictional resistance at times was 600 lbs. per sq. ft. 
At Cairo, in sand and gravel, the normal friction was about 600 lbs. 
per sq. ft. 

For data on the friction of iron cylinders and masonry shafts, 
see §§ 418-19, pages 275-77; and for data on the friction of ordi¬ 
nary piles, see §§ 370-72, pages 247-48. 

456. Filling the Air-chamber. When the caisson has 
reached the required depth, the bottom is leveled off—by blasting, 
if necessary,—and the working chamber and shafts are filled with 
concrete. Sometimes only enough concrete is placed in the bottom 
to seal the chamber water-tight, and the remaining space is filled 
with sand. This was done at the east abutment of the St. Louis 
bridge, the sand being pumped in from the river with the sand- 
pump previously used for excavating the material from under the 
caisson. 

457. Noted Examples. The St. Louis Bridge. The founda¬ 
tions of the steel-arch bridge over the Mississippi at St. Louis are 
the deepest ever sunk by the pneumatic process, and at the time of 
construction (1870) they were also very much the largest. The 
caisson of the east abutment was an irregular hexagon in plan, 
83 X 70 feet at the base, and 64 X 48 feet at the top—14 feet above 
the cutting edge. The working chamber was 9 feet high. The 
cutting edge finally rested on the solid rock 94 feet below low 
water. The maximum emersion was 109 feet 8-J- inches, the greatest 
depth at which pneumatic work has yet been done. The other 

caissons were almost as large as the one mentioned above, but were 

% 

not sunk as deep. 

The caissons wore constructed mainly of wood ; but the side 



293 


FOUNDATIONS UNDER WATER. 


[CHAP. XII. 


walk and the roof were covered with plate iron to prevent leakage, 
and strengthened by iron girders on the inside. This was the first 
pneumatic caisson constructed in America; and the use of large 
quantities of timber was an important innovation, and has become 
one of the distinguishing characteristics of American practice. In 
all subsequent experience in this country (except as mentioned in 
§ 458), the iron lining for the working chamber has been dispensed 
with. The masonry rested directly upon the roof of the caisson, 
i. e., no crib-work was employed. In sinking the first pneumatic 
foundation an iron coffer-dam was built upon the top of the caisson ; 
but the last—the largest and deepest—was sunk without a coffer¬ 
dam,—a departure from ordinary European practice, which is occa¬ 
sionally followed in this country (see § 436). * 

458. The Brooklyn Bridge. The foundations of the towers of 
the suspension bridge over the East River, between New York City 
and Brooklyn, are the largest ever sunk by the pneumatic process. 
The foundation of the New York tower, which was a little larger 
and deeper than the other, was rectangular, 172 X 102 feet at the 
bottom of the foundation, and 157 X 77 feet at the bottom of the 
masonry. The caisson proper was 31| feet high, the roof being a 
solid mass of timber 22 feet thick. The working chamber was 9| 
feet high. The bottom of the foundation is 78 feet below mean 
high tide, and the bottom of the masonry is 46J feet below the 
same. From the bottom of the foundation to the top of the 
balustrade on the tower is 354 feet, the top of the tower being 276 
feet above mean high tide. 

To make the working chamber air-tight, the timbers were laid 
in pitch and all seams calked ; and in addition, the sides and the 
roof were covered with plate iron. As a still further precaution, 
the inside of the air-chamber was coated with varnish made of rosin, 
menhaden oil, and Spanish brown. 

For additional details see the several annual reports of the en¬ 
gineers in charge, and also numerous articles in the engineering 
newspapers and magazines from 1869 to 1872. 

459. Forth Bridge. For an illustrated account of the pneumatic 
foundation work of the bridge across the Frith of Forth, Eng¬ 
land, see Engineering News , vol. xiii. pages 242-43. The caissons 
employed there differed from those described above (1) in being 
made almost wholly of iron, (2) in an elaborate system of cages for 



ART. 4.] 


PNEUMATIC PROCESS. 


209 


hoisting the material from the inside, and (3) in the use of inter¬ 
locked hydraulic apparatus to open and close the air-locks. Each 
of the two deep-water piers consists of four cylindrical caissons 
70 feet in diameter the deepest of which rests 96 feet below high 
tide. 

460. Physiological Effect of Compressed Air. In the ap¬ 
plication of the compressed-air process, the question of the ability 
of the human system to bear the increased pressure of the air be¬ 
comes very important. 

After entering the air-lock, as the pressure increases, the first 
sensation experienced is one of great heat. As the pressure is still 
further increased a pain is felt in the ear, arising from the abnormal 
pressure upon the ear-drum. The tubes extending from the back 
of the mouth to the bony cavities over which this membrane is 
stretched, are so very minute that compressed air can not pass 
through them with a rapidity sufficient to keep up the equilibrium 
of pressure on both sides of the drum (for which purpose the tubes 
were designed by nature), and the excess of pressure on the outside 
causes the pain. These tubes can be distended, thus relieving the 
pain, by the act of swallowing, or by closing the nostrils with the 
thumb and finger, shutting the lips tightly, and inflating the 
cheeks. Either action facilitates the passage of the air through 
these tubes, and establishes the equilibrium desired. The relief is 
only momentary, and the act must be repeated from time to time, 
as the pressure in the air-lock increases. This pain is felt only 
while the air in the lock is being “ equalized,” i. e., while the air is 
being admitted, and is most severe the first time compressed air is 
encountered, a little experience generally removing all unpleasant 
sensations. The passage through the lock, both going in and com¬ 
ing out, should be slow; that is to say, the compressed air should 
be let in and out gradually, to give the pressure time to equalize 
itself throughout the various parts of the body. 

When the lungs and whole system are filled thoroughly with 
the denser air, the general effect is rather bracing and exhilarating. 
The increased amount of oxygen breathed in compressed air very 
much accelerates the organic functions of the body, and hence labor 
in the caisson is more exhaustive than in the open air; and on get¬ 
ting outside again, a reaction with a general feeling of prostration 
.sets in. At moderate depths, however, the laborers in the caisson, 



300 


FOUNDATIONS UNDER WATER. 


[CHAP. XII- 


after a little experience, feel no bad effects from the compressed air,, 
either while at work or afterwards. 

Remaining too long in the working chamber causes a form of 
paralysis, recently named caisson disease, which is sometimes fatal. 
The injurious effect of compressed air is much greater on men ad¬ 
dicted to the use of intoxicating liquors than on others. Only 
sound, able-bodied men should be permitted to work in the caisson. 

In passing through the air-lock on leaving the air-chamber, the 
workman experiences a great loss of heat owing (1) to the expan¬ 
sion of the atmosphere in the lock, (2) to the expansion of the free 
gases in the cavities of the body, and (3) to the liberation of the 
gases held in solution by the liquids of the body. Hence, on com¬ 
ing out the men should be protected from currents of air, should 
drink a cup of strong hot coffee, dress warmly, and lie down for a 
short time. 

461. No physiological difficulty is encountered at small depths; 
but this method is limited to depths not much exceeding 100 feet, 
owing to the deleterious effect of the compressed air upon the work¬ 
men. At the east abutment of the St. Louis bridge (§ 457), the 
caisson was sunk 110 feet below the surface of the water. Except 
in this instance, the compressed-air process has never been applied 
at a greater depth than about 90 feet. Theoretically, the depth, in 
feet, of the lower edge of the caisson below the surface divided by 
33 is equal to the number of atmospheres of pressure. The press¬ 
ure is never more than this, and sometimes, owing to the fric¬ 
tional resistance to the flow of the water through the soil, it is a 
little less. Therefore the depth does not exactly indicate the 
pressure ; but the rule is sufficiently exact for this purpose. At St. 
Louis, at a depth of 110 feet, the men were able to work in the 
compressed air only four hours per day in shifts of two hours each, 
and even then worked only part of the time they were in the air- 
chamber. 

With reasonable care, the pneumatic process can be applied at 
depths less than 80 or 90 feet without serious consequences. At 
great depths the danger can be greatly decreased by observing the 
following precautions, in addition to those referred to above : (1) In 
hot weather cool the air before it enters the caisson ; * (2) in cold 

* This was done in 1888 at the bridge over the Ohio River at Cairo, Ill.—prob¬ 
ably the first example. The temperature of the air was reduced 30° F. 






ART. 4.] PNEUMATIC PROCESS. 301 

weather warm the air in the lock when the men come out; and 
(3) raise and lower them by machinery. 

For an exhaustive account of the various aspects of this subject, 
see Dr. Smithes article on the “ Physiological Effect of Compressed 
Air,” in the Report of the Engineer of the Brooklyn Bridge.* 

462. COST. The contract for pneumatic foundation is usually 
let at specified prices per unit for the materials left permanently in 
the structure and for the material excavated, including the neces¬ 
sary labor and tools. The prices for material in place are about as 
follows : Timber in caisson proper, from $40 to $50 per thousand 
feet, board measure, according to the locality in which the work is 
done ; and the timber in the crib-work and coffer-dam about $5 to 
$7 per thousand less. The concrete, which is usually composed of 
broken stone and sufficient 1 to 2 or 1 to 3 Portland cement mortar 
to completely fill the voids, costs, exclusive of the cement, from $5 to 
$7 per cubic yard for that in the crib, and about twice this sum for 
that in the air-chamber and under the cutting edge. The wrought- 
iron spikes, drift-bolts, screw-bolts, and cast-iron washers cost from 
3^ to 6 cents per pound, f The caisson and filling costs from $14 to 
$20 per cubic yard ; and the crib and filling from $8 to $10. 

The price for sinking, including labor, tools, machinery, etc., 
ranges, according to the kind of soil, from 18 to 40, or even 50, 
cents per cubic foot of the volume found by multiplying the area 
of the caisson at the cutting edge by the final depth of the latter 
below low water. In sand or silt the cost is 18 to 20 cents, and in 
stiff clay and bowlders 40 to 50 cents. 

463. Examples. The table on page 302 gives the details of the 
cost of the pneumatic foundation of the Havre de Grace bridge, as 
fully described in §§ 438-44. 

The table on page 303 gives the details of the cost of the pneu¬ 
matic caissons of the bridge across the Missouri River near Blair, 
Neb. The caissons (Fig. 65, page 285) were 54 feet long, 24 feet wide, 
and 17 feet high. In the two shore piers, Nos. I and IV of the 
table, the caissons were surmounted by cribs 20 feet high ; but in 
the channel piers, the masonry rested directly upon the roof of the 


* Prize Essay of the Alumni Association of the College of Physicians and Sur¬ 
geons of New York City, 1873. 

f There are usually from 140 to 150 pounds of iron per thousand feet (board meas¬ 
ure) of timber. 









302 


FOUNDATIONS UNDER WATER. 


[CHAP. XII. 


TABLE 32. 

Cost, to the R. R. Co., of Foundations of Havre de Grace Bridge.* 


Items. 


Number of the 

Pier. 


II. 

III. 

IV. 

VIII. 

IX. 

Depth of cutting edge below low water. 






feet . 

68.3 

70.7 

59.9 

76.0 

65.0 

Depth of cutting edge below mud line. 






feet.. 

55.5 

58.7 

32.3 

55.2 

32.6 

Displacement below low water, cu. ft. 

112,124 

123,402 

159,588 

189,578 

231,691 

“ mud line, cu. ft.. 

94,504 

106,269 

84,014 

127,586 

107,836 

Caisson: timber, $46.80 per M. 

$9,522.54 

$10,088.44 

$14,820.94 

$13,176.07 

$21,767.85 

iron, @ 5J4 cts. per lb....__ 

1.456.12 

1,587.15 

2,596.23 

2.242.40 

3.295.38 

concrete. @ $17.50 per cu. yd. 

5,775.00 

7,017.50 

13,247.50 

18,987.50 

25,602.50 

total cost, per net cu. yd. 

16.82 

18.37 

19.19 

24.34 

22.10 

Crib : timber, @ $46.80 per M. 

8,421.14 

9.262.19 

6.738.87 

8,936.58 

9,538.96 

iron, 5J4 cts. per lb. 

1,291.14 

1,454.85 

1,179.36 

1.749.35 

1,445.93 

concrete, @ $8.50 per net cu. yd.. 

14,016.50 

16,090.50 

13,897.50 

21.943.50 

26,962.00 

total cost, per cu. yd. 

10.16 

11.10 

10.91 

9.91 

10.09 

Coffer-dam: timber, @ $46 80 per M. 

96.78 

1.375.00 

5,078.64 

4,013.52 

5.921.70 

iron, @ 514 cts. per lb. 

14.45 

236.15 

892.29 

684.20 

899.22 

Cost of sinking, @ 20 cts. per cu. ft. of 






displacement below low water. 

22,424.80 

24.680.40 

31.917 60 

37,915 60 

46,338 20 

Concrete below cutting edge, @ $17.50 .. 

000 

10,902.50 

2,205 00 

9,205.00 

10,920.00 

Total cost of foundation . 

Total cost per cu. yd. of foundation be¬ 
low masonry, including coffer-dams. 

63,018.47 

19.93 

71,792.18 

21.58 

90,368.93 

25.20 

109,648.72 

23.30 

141,772.44 

23.44 


Average total cost of the foundation, to R. R. Co., per net cubic yard.$22.69. 


caisson. The work was clone, in 1882-83, by the bridge company's 
men under the direction of the engineer. 

464. In 1869-72, thirteen cylinders were sunk by the plenum- 
pneumatic process for the piers of a bridge over the Schuylkill 
River at South Street, Philadelphia. There were three piers, one 
of which was a pivot pier. There were two cylinders, 8 feet in 
diameter and 82 feet long, sunk through 22 feet of water and 30 
feet of “ sand and tough compact mud intermingled with bowlders 
two cylinders, 8 feet in diameter and 57 feet long, sunk through 22 
feet of water and 5 feet of soil as above ; one cylinder, 6 feet in 
diameter and 64 feet long, sunk through 22 feet of water and 18 
feet of soil as above ; and 8 columns, 4 feet in diameter and aggre¬ 
gating 507 feet, sunk through 22 feet of water and 18 feet of soil 
as above. A 10-foot section of the 8-foot cylinder weighed 14,600 
pounds, of the 6-foot, 10,800 pounds, and of the 4-foot, 6,800 
pounds. The cylinders rested upon bed-rock, and were bolted to 

* Data by courtesy of Sooysmith & Co., contracting engineers for the pneumatic 
foundations. 








































ART. 4.] 


PNEUMATIC PROCESS. 


303' 


it. The actual cost to the contractor, exclusive of tools and ma¬ 
chinery, was as in Table 34 (page 304). 


TABLE 38. 

Cost of Pneumatic Foundations of Blair Bridge.* 


Items. 

Number of 

the Pier. 

I. 

II. 

III. 

IV. 

Total distance caisson was lowered after comple- 





tion. 

55.6 ft. 

54.5 ft. 

56.2 ft. 

68.5 ft. 

Final depth of cutting edge below surface of water 

51.9 “ 

52.3 “ 

53.4 “ 

57.0 “ 

“ “ “ “ ** “ mud line. 

47.7 " 

51.0 “ 

49.4 “ 

54.7 u 

Caisson and filling, cost of. 

$11,753.51 

$12,386.56 

$13,819.34 

$11,252.45 

“ “ *• “ “ per cubic yard . 

14.31 

15.12 

16.74 

13.77 

Crib find filling cost of .. 

7,368.16 



6,303.46 

“ “ “ “ “ per cubic yard . 

8.85 



7.59 

Air-lock, shafts, etc., cost of. 

1,481.60 

1,567.42 

1,536.80 

1,521.08 

Sinking caisson, cost of, including erection and re- 





moval of machinery. 

5,772.52 

5,629.37 

6,888.16 

7,084.26 

Sinking caisson, cost of, per cubic foot of displace- 





ment below position of cutting edge when 





caisson was completed. 

8.0 cts. 

8.0 cts. 

9.5 cts. 

7.1 cts. 

Sinking caisson, cost of, per cubic foot of displace- 





ment below surface of water .. 

8.6 “ 

8.3 “ 

9.9 “ 

9.6 kl 

Sinking caisson, cost of, per cubic foot of displace- 





ment below mud line. 

9.3 “ 

8.5 “ 

10.8 “ 

10.0 lk 

Total cost t of foundation. 

$26,375.79 

$19,583.35 

$22,244.30 

$26,161.25 

“ “ “ “ per cubic yard. 

15.98^ 23.87 

27.08 

15.85 


Average costt of the foundations, per cubic yard..$20.70. 


465. “Excavation in the Brooklyn caisson l cost for labor 
only, including the men on top, about 15.25 per cubic yard 
[19 cents per cubic foot]. Running the six air-compressors 
added to this $3.60 per hour, or about 47 cents per yard ; lights 
added $0.56 more; and these with other contingencies nearly 
equaled the cost of labor. The great cost was due to the excessive 
hardness of the material over much of the surface, the caisson finally 
resting, for nearly its whole extent, on a mass of bowlders or hard- 
pan. The concrete in the caisson cost, for every expense, about 

* Compiled from the report of Geo. S. Morison, chief engineer of the bridge. 

t Exclusive of engineering expenses and cost of tools, machinery, and buildings. 
In a note to the author, Mr. Morison, the engineer of the bridge says : “ It is impos¬ 
sible to divide the buildings, tools, and engineering expenses between the substruct¬ 
ure and other portions of the work. The bulk of the items of tools and machineij 
[$12,369.88], however, relates to the foundations.” The engineering expenses and 
buildings were nearly 3 per cent, of the total cost of the entire bridge. The cost of 
tools and machinery was equal to a little over 13 per cent, of the cost of the founda¬ 
tions as above. Including these items would add nearly one sixth to the amounts in 

the last three lines. 

% For a brief description, see § 458. 



































.304 


FOUNDATIONS UNDER WATER. 


[CHAP. XII. 


TABLE 34. 

Cost of Pneumatic Piles at Philadelphia in 1869-72.* 


Diameter of Cylinders 


Items of Expense. 

4-ft. 

6-ft. 

8 ft. 

Cost of cast iron, $59.50 per ton. 

$11,239.36 

489.84 

1,266.79 

6,693.50 

$2,053.75 

93.31 

358.40 

911.88 

$13,577.90 

670.02 

2,779.97 

9.036.51 

“ “ bolts, @ cents per lb. 

“ “ grouted"rubble masonry (exclusive of labor), $5.40 

per cu. yd. 

“ “ sinking, and laying masonry. 

Total cost of the cylinders in place. 

$19,689.49 

$23.10 

2.50 

13.20 

$3,417.34 

$33.54 

5.60 

14.25 

$26,064.40 

$51.25 

10.00 

32.51 

Cost of iron per lineal foot of cylinder . 

“ “ materials for masonry per lineal foot of cylinder_ 

“ “ sinking and laying masonry per lineal foot of cylinder 

Total cost,t per lineal foot, of cylinder in place . 

$38.80 

$53.39 

$93.76 



$15.50 per cubic yard. The caisson and filling together aggregated 
16,898 cubic yards ; and the approximate cost per yard for every 
expense was $20.71."]! The foundation therefore cost about $30 
per cubic yard. 

The pneumatic foundations for the channel piers of the bridge 
over the Missouri at Plattsmouth, Neb., cost as follows: One 
foundation, consisting of a caisson 50 ft. long, 20 ft. wide, and 15.5 
ft. high, surmounted by a crib 14.15 ft. high, sunk through 13 ft. 
of water and 20 ft. of soil, cost $19.29 per cubic yard of net volume. 
Another, consisting of a caisson 50 ft. long, 20 ft. wide, and 15.5 
ft. high, surmounted by a crib 36.25 ft. high, sunk through 10 
ft. of water and 44 ft. of soil, cost $14.45 per cubic yard of net 
volume. § 

466. European Examples. The following * * * § |[ is interesting as 
showing the cost of pneumatic work in Europe : 

“ At Moulins, cast-iron cylinders, 8 feet 2 J inches in diameter, 
with a filling of concrete and sunk 33 feet below water into marl, 
cost $62.94 per lineal foot, or $29.71 for the iron work, and $33.23 


* Compiled from an article by D. McN. Stauffer, engineer in charge, in Trans. Am. 
Soc. of C. E., vol. vii. pp. 287-309. 

t Exclusive of tools and machinery. 

X F. Collingwood, assistant engineer Brooklyn bridge, in Trans. Am. Soc. of C. E. 

§ Compiled from the report of Geo. S. Morison, chief engineer of the bridge. 

If By Jules Gaudard, as translated from the French by L. F. Vernon-Harcourt for 
the Proceedings of the Institute of Civil Engineers (London). 






























ART. 4.] 


PNEUMATIC PROCESS. 


305 


for sinking and concrete. At Argenteuil, with cylinders 11 feet 10 
inches in diameter, the sinking alone cost $42.12 per lineal foot 
[nearly $10 per cubic yard], where a cylinder was sunk 53J feet in 
three hundred and ninety hours. [The total cost of this founda¬ 
tion was $34.09 per cubic yard, see table on page 310.] At Orival, 
where a cylinder was sunk 49 feet in twenty days, the cost of sinking 
was $36.83 per lineal foot. At Bordeaux, with the same-sized 
C}dinders, a gang of eight men conducted the sinking of one cylim 
der, and usually 34 cubic yards were excavated every twenty-four 
hours. The greatest depth reached was 55f feet below the ground, 
and 71 feet below high water. In the regular course of working, a 
cylinder was sunk in from nine to fifteen days, and the whole opera¬ 
tion, including preparations and filling with concrete, occupied on 
the average 25 days. One cylinder, or a half pier, cost on the aver¬ 
age $11,298.40, of which $1,461 was for sinking. M. Morandiere 
estimates the total cost of a cylinder sunk like those at Argenteuil, 
to a depth of 50 feet, at $7,012.80. 

467. “ Considering next the cost of piers of masonry on wrought- 
iron caissons of excavation, the foundations of the Lorient viaduct 
over the Scorff cost the large sum of $24.11 per cubic yard, owing to 
difficulties caused by the tides, the labor of removing the bowlders 
from underneath the caisson, and the large cost of plant for only 
two piers. The foundation of the Kehl bridge cost still more, about 
$28.23 * per cubic yard ; but this can not be regarded as a fair in¬ 
stance, being the first attempt [see § 429] of the kind. 

“The foundations of the Nantes bridges, sunk 56 feet below 
low-water level, cost about $14.84 per cubic yard. The average 
cost per pier was as follows : 


Caisson (41 feet 4 inches by 14 feet 5 inches), 50 tons of wrought 

iron @ $116.88. 

Coffer-dam, 3 tons of wrought iron @ $58.44. 

Excavation, 916 cubic yards @ $4.47. 

Concrete. . 

Masonry, plant, etc. 

Average cost per pier. 


$5,844 

175 

4,091 

4,188 

1,870 


$16,168 


“One pier of the bridge over the Meuse at Rotterdam, with a 


* Notice the slight inconsistency between this quantity and the one in the third 
line from the last of the table on page 310, both being from the same article. 











306 


FOUNDATIONS UNDER WATER. 


[CHAP. XII- 


caisson of 222 tons and a coffer-dam casing of 94 tons, and sunk 75- 
feet below high water, cost $70,858, or $13.97 per cubic yard. 

“The Vichy bridge has five piers built on caissons 34 feet by 13- 
feet, and two abutments on caissons 26 feet bv 24 feet. The foun- 
dations were sunk 23 feet in the ground, the upper portion con¬ 
sisting of shingle and conglomerated gravel, and the last 10 feet of 
marl. The cost of the bridge was as follows : 


Interest for eight months, and depreciation of plant worth $19,480.. $3,896 

Cost of preparations, approach bridge, and staging. 4,904 

Caissons (seven), 150£ tons @ $113.38. 17,108 

Sinking. 9,823 

Concrete and masonry. 5,303 

Contractor’s bonus and general expenses. 6,107 


Total cost of five foundations. $47,141 


The cost per cubic yard of the foundation below low water "was 
$16.69, of which the sinking alone cost $3.50 in gravel, and $4.37 
in marl. 

“At St. Maurice, the cost per cubic yard of foundation was 
$15.94, exclusive of staging.” 

468. Conclusion. Except in very shallow or very deep water, 
the compressed-air process has almost entirely superseded all others. 
The following are some of the advantages of this method. 1. It is 
reliable, since there is no danger of the caisson’s being stopped, 
before reaching the desired depth, by sunken logs, bowlders, etc., 
or by excessive friction, as in dredging through tubes or shafts in 
cribs. 2. It can be used regardless of the kind of soil overlying the 
rock or ultimate foundation. 3. It is comparatively rapid, since 
the sinking of the caisson and the building up of the pier go on at 
the same time. 4. It is comparatively economical, since the weight 
added in sinking is a part of the foundation and is permanent, and 
the removal of the material by blowing out or by pumping is as 
uniform and rapid at one depth as at another,—the cost only being 
increased somewhat by the greater depth. 5. This method allows 
ample opportunity to examine the ultimate foundation, to level the 
bottom, and to remove any disintegrated rock. 6. Since the rock 
can be laid bare and be thoroughly washed, the concrete can be com¬ 
menced upon a perfectly clean surface ; and hence there need be no 
question as to the stability of the foundation. 










ART. 5.] 


THE FREEZING PROCESS. 


30? 


Art. 5. The Freezing Process. 

469. Principle. The presence of water has always been the 
great obstacle in foundation work and in shaft sinking, and it 
is only very recently that any one thought of transforming the 
liquid soil into a solid wall of ice about the space to be excavated. 
The method of doing this consists in inclosing the site to be ex¬ 
cavated, by driving into the ground a number of tubes through 
which a freezing mixture is made to circulate. These consist of a 
large tube, closed at the lower end, inclosing a smaller one, open at 
the lower end. The freezing mixture is forced down the inner 
tube, and rises through the outer one. At the top, these tubes 
connect with a reservoir, a refrigerating machine, and a pump. 
The freezing liquid is cooled by an ice-rhaking machine, and then 
forced through the tubes until a wall of earth is frozen around 
them of sufficient thickness to stand the external pressure, when 
the excavation can proceed as in dry ground. 

470. History. This method was invented by F. H. Poetsch, 
M.D., of Aschersleben, Prussia, in 1883. It has been applied in 
but three cases. The first was at the Archibald colliery, near 
Schweidlingen, Prussia, where a vein of quicksand, 20 feet thick, was 
encountered at a depth of about 150 feet below the surface. Here 
twenty-three pipes were used, and 35 days consumed in the freezing 
process, under local difficulties. The second was at the Centrum 
mine, near Berlin, where about 107 feet of quicksand, etc., was 
penetrated. Engineers had been baffled for years in their attempts 
to sink a shaft here; but in 33 days Mr. Poetsch had, with only 16 
freezing tubes, secured a 6-foot wall of ice around the shaft area, and 
the shaft was excavated and curbed without difficulty. The third 
piece of work was at the Eimilia mine, Fensterwalde, Austria, in 
1885, where an 8£-foot shaft was sunk through 115 feet of quick¬ 
sand.* 

471. Details of the Process. In the last case mentioned 
above, “12 circulatory tubes were used, sunk in a circle about 14 
feet in diameter, from 12 to 15 days being required to sink them a 
depth of about 100 feet. The outside tubes were 8£ inches in 

* As this volume is going through the press, this method is being applied in two 
places in this country—Iron Mountain, Mich., and Wyoming, Penn.—in sinking 
mine-shafts. 





V 


308 FOUNDATIONS UNDER WATER. [CHAP. XII. 

diameter, and made of plate iron 0.15 inch thick. The tubes were 
sunk by aid of the water-jet. They were given a very slight incli¬ 
nation outward at the bottom to avoid any deviation in sinking 
that might interfere with the line of the shaft. The freezing 
liquid employed was a solution of chloride of calcium, which con¬ 
geals at a temperature of —35° C. ( —31° F.). The circulation of 
the liquid through the tubes was secured by a small pump with 
a piston 6 inches in diameter and a 12-inch stroke. At the begin¬ 
ning of the operation, this pump made 30 double strokes per min¬ 
ute, which was equivalent to the passage of 0.6 gallon of the liquid 
through each tube per minute; at the end of the operation, when 
it was only necessary to maintain the low temperature, the pump 
strokes were reduced to 15 per minute. The refrigerating machine 
employed was one of a model guaranteed by the maker to produce 
1,100 pounds of ice per hour. The motive-power was supplied by 
a small engine of about 5 horse-power. The ammoniac pump had 
a piston 2.8 inches in diameter and a 9.2-inch stroke, and made 30 
strokes per minute. The pressure maintained was about 10 atmos¬ 
pheres. The quantity of ammoniacal liquid necessary to charge 
the apparatus was 281 gallons; and under normal conditions the 
daily consumption of this liquid was 0.78 gallon. 

“ The actual shaft excavation was commenced 53 days after the 
freezing apparatus had been set in motion. The freezing machine 
was in operation 240 days. The work was done without difficulty, 
and a progress of 1.64 feet per day was made. The timbering was 
very light, but no internal pressure of any kind was observed. The 
brick masonry used for finally lining the shaft was about 11 inches 
thick. When the shaft was finished, the tubes were withdrawn 
without difficulty, by circulating through them a hot, instead of a 
cold, solution of the chloride of calcium, thus thawing them loose 
from the surrounding ice. The tubes were entirely uninjured, and 
could be used again in another similar operation. 

472. “ The material in the above plant is estimated to have cost 
115,000, and $4,800 more for mounting and installation. The daily 
expense of conducting the freezing process is estimated at $11. The 
total expense for putting down the shaft is estimated at $128.66 per 
linear foot.” * The last is equivalent to about $2.25 per cubic foot. 

* Engineering News, vol. xiv. pp. 24, 25, translated from Le Genie Civil of June 13, 
1885. 








ART. 6.] 


COMPARISON OF METHODS. 


30b 


473 . Modification for Foundations under Water. For sinking 

loundations under water, two methods of applying this process have 
been proposed. One of these consists in combining the pneumatic 
and freezing processes. A pneumatic caisson is to be sunk a short 
distance into the river-bed, and then the congealing tubes are 
applied, and the entire mass between the caisson and the rock is 
frozen solid. When the freezing is completed, the caisson will be 
practically sealed against the entrance of water, and the air-lock can 
be removed and the masonry built up as in the open air. 

The other method consists in sinking an open caisson to the 
river-bed, and putting the freezing tubes down through the water. 
When the congelation is completed, the water can be pumped out 
and the work conducted in the open air. 

474 . Advantages Claimed. It is claimed for this process that 
it is expeditious and economical, and also that it is particularly 
valuable in that it makes possible an accurate estimate of the total 
cost before the work is commenced,—a condition of affairs unat¬ 
tainable by any other known method in equally difficult ground. It 
has an advantage over the pneumatic process in that it is not limited 
by depth. It can be applied horizontally as well as vertically, and 
hence is specially useful in sub-aqueous tunneling, particularly in 
soils which, with compressed air, are treacherous. 

475 . Difficulties Anticipated. So far it has been used only 
in sinking shafts for mines. Two difficulties are anticipated in ap¬ 
plying it to sink foundations for bridge piers in river beds ; viz., 
(1) the difficulty in sinking the pipes, owing to striking sunken logs, 
bowlders, etc.; and (2) the possibility of encountering running 
water, which will thaw the ice-wall. These difficulties are not in¬ 
surmountable, but experience only can demonstrate how serious 
they are. 

476 . Cost. See § 472, and compare with table on page 310 . 

Art. 6. Comparison of Methods. 

477 . The following comparison of the different methods is from 
an article by Jules Gaudard on Foundations, as translated by L. F. 
Vernon-Harcourt for the proceedings of the Institute of Civil Em 
gineers (London). Except as showing approximate relative costs in 
Europe, it is not of much value, owing to improvement made since 
the article was written, to the differences between European and 



310 


FOUNDATIONS UNDER WATER. 


[CHAP. XII* 


American practice, and to differences in cost of materials in the two 
countries. 

478. “ M. Croizette Desnoyers has framed a classification of the 
methods of foundations most suitable for different depths, and also 
an estimate of the cost of each. • These estimates, however, must be 
considered merely approximate, as unforeseen circumstances pro¬ 
duce considerable variations in works of this nature. 


TABLE 35. 

Cost of Various Kinds of Foundations in Europe. 


Kind of Foundation. 


On pile# 1 after compression of the ground, shallow depth. 
“ “ “ “ “ “ “ greater depth 


By sinking wells. 
By pumping. 


under favorable circumstances.... 
“ “ unfavorable circumstances. 

Ou concrete under water, small amount of silt. 
“ “ “ “ large “ “ “ . 


By means of compressed air* under favorable circumstances... 
* “ “ “ “ “ unfavorable circumstances: 

Lorient viaduct. 

• Kehl bridge t. 

Argenteuil bridge. 

Bordeaux bridge. 


Depth 
in Feet. 


Min. 


20 

33 

33 


26 

26 

20 

20 


Max. 


33 

50 

50 

20 

33 

33 

33 

33 


50 ft. 
70 “ 
50 


Cost per 
Cubic Yard. 


Min. 


$2.92 

4.39 

7.30 

2.92 

4.39 

14.85 

4.37 

9.00 

13.39 


Max. 


$4.39 

7.30 

9.00 

4.39 

13.39 

17.77 

9.00 

11.93 


16.17 


$24.11 

29.71 

34.09 

40.17 


* See also §§ 466-67. t See foot-note on page 305. 

r 

“When the foundations consist of disconnected pillars or piles, 
the above prices must be applied to the whole cubic content, includ¬ 
ing the intervals between the parts ; but of course at an equal cost 
solid piers are the best. 

479. “For pile-work foundations the square yard of base is prob¬ 
ably a better unit than the cubic yard. Thus the foundations of 
the Vernon bridge, with piles from 24 to 31 feet long, and with 
cross-timbering, concrete, and caisson, cost $70 per square yard of 
base. According to estimates made by M. Picquenot, if the foun¬ 
dations had been put in by means of compressed air, the cost would 
have been $159.64 ; with a caisson, not water-tight, sunk down, 
$66.27 ; with concrete poured into a space inclosed with sheeting, 
$62.23 ; and by pumping, $83.56 per square yard of base.” 
































PART IV. 


MASONRY STRUCTURES. 


CHAPTER XIII. 

MASONRY DAMS. 

480. It is not the intention here to discuss every feature of 
masonry dams; that has been done in the special reports and arti¬ 
cles referred to in § 520, page 334. The fundamental principles 
will be considered, particularly with reference to their applica¬ 
tion in the subsequent study of retaining walls, bridge abutments, 
bridge piers, and arches. The discussions of this chapter are 
applicable to masonry dams, reservoir walls, or to any wall which 
counteracts the pressure of water mainly by its weight. 

There are two ways in which a masonry dam may resist the 
thrust of the water ; viz., (1) by the inertia of its masonry, and 
(2) as an arch. 1. The horizontal thrust of the water may be held 
in equilibrium by the resistance of the masonry to sliding forward 
or to overturning. A dam which acts in this way is called a gravity 
dam. 2. The thrust of the water may be resisted by being trans¬ 
mitted laterally to the side-hills (abutments) by the arch-like action 
of the masonry. A dam which acts in this way is called an arched 
dam. 

Only two dams of the pure arch type have ever been built. The 
almost exclusive use of the gravity type is due to the uncertainty 
of our knowledge concerning the laws governing the stability of 
masonry arches. This chapter will be devoted mainly to gravity 
dams, those of the arch type being considered only incidentally. 
Arches will be discussed fully in Chapter XVIII. 


311 



312 


MASONRY DAMS. 


[CHAP. XIII. 


Art. 1. Stability of Gravity Dams. 

481. Principles. By the principles of hydrostatics we know 
(1) that the pressure of a liquid upon any surface is equal to tho 
weight of a volume of the liquid whose base is the area of the im¬ 
mersed surface and whose height is the vertical distance of the center 
of gravity of that surface below the upper surface of the water ; (2) 
that tliis pressure is always perpendicular to the pressed surface ; 
and (3) that, for rectangular surfaces, this pressure may be con¬ 
sidered as a single force applied at a distance below the upper 
surface of the liquid equal to f of the depth. 

482. A gravity dam may fail (1) by sliding along a horizontal 
joint, or (2) by overturning about the front of a horizontal joint, 
or (3) by crushing the masonry, particularly at the front of 
any horizontal joint. However, it is admitted that by far the 
greater number of failures of dams is due to defects in the founda¬ 
tion. The method of securing a firm foundation has already been 
discussed in Part III; and, hence, this subject will be considered 
here only incidentally. There is not much probability that a dam 
will fail by sliding forward, but it may fail by overturning or by the 
crushing of the masonry. These three methods of failure will be 
considered separately and in the above order. 

483. In the discussions of this article jt will be necessary to 
consider only a section of the wall included between two vertical 
planes—a unit distance apart—perpendicular to the face of the 
wall, and then so arrange this section that it will resist the loads and 
pressure put upon it; that is, it is sufficient, and more convenient, 
to consider the dam as only a unit, say 1 foot, long. 

484. Nomenclature. The following nomenclature will be used 
throughout this chapter : 

H = the horizontal pressure, in pounds, of the water against a 
section of the back of the wall 1 foot long and of a height, 
equal to the height of the wall. 

W = the weight, in pounds, of a section of the wall 1 foot long. 

w = the weight, in pounds, of a cubic foot of the masonry. 

h = the height, in feet, of the wall; i. e., h = E F, Fig. 68. 

I — the length of the base of the cross section; i. e., I — A B y 
Fig. 68. 

t =■ the width of the wall on top ; i. e., t = D E, Fig. 68. 



ART. 1.] 


STABILITY OF GRAVITY DAMS. 


313 


b = the batter of the wall, i. e., the inclination of the surface 
per foot of rise —V being used for the batter of the up- 
__ stream face and b x for that of the down-stream face. 
x =■ A C — the distance from the down-stream face of any joint to 
the point in which a vertical through the center of gravity 
of the wall pierces the plane of the base. 
d ~ the distance the center of pressure deviates from the center 
of the base. 

62.5 = the weight, in pounds, of a cubic foot of water. 

485. Stability against Sliding. The horizontal pressure of 
the water tends to slide the dam forward, and is resisted by the 
friction due to the weight of the wall. 

486. Sliding Force. The horizontal pressure of the water 
against an elementary section of the wall, by principle (1) of § 481, 
is equal to the area of the section multiplied by half the height of 
the wall, and that product by the weight of a cubic unit of water; or 


H = h X 1 Xih X 62.5 = 31.25 Id. . . . (1) 


Notice that H is the same whether the pressed area is inclined or 
vertical; that is to say, H is the horizontal component of the total 
pressure on the surface. 

487. Resisting Forces. The weight of an elementary section of 
the wall is equal to the area of the vertical 
cross section multiplied by the weight of a 
cubic unit of the masonry. The area of 
the cross section, ABED, Fig. 68, equals 

EFxDF+iEFxFB+\D GxAG 

^Kt+ildb'+ildb, ... ( 2 ) 

Then the weight of the elementary sec¬ 
tion of the wall is 


W = w (h t + i Id b' + i Id b,) 



ac f 


The vertical pressure of the water on Fig. 68. 

the inclined face increases the pressure on the foundation, and, 
consequently, adds to the resistance against sliding. The vertical 
pressure on FB is equal to the horizontal projection of that area 
multiplied by the distance of the center of gravity of the surface 
below the top of the water and by the weight of a cubic unit of 

















314 


MASONRY DAMS. 


[CHAP. XIII. 


water, or, the vertical pressure = F B X 1 X \li X 62.5 — hF X 
62.5 = 31.25 Id F. 

488. If the earth rests against the heel of the clam (the bot¬ 
tom of the inside face), it will increase the pressure on the foun¬ 
dation, since earth weighs more than water ; on the other hand, the 
horizontal pressure of the earth will be a little greater than that of 
an equal height of water. However, since the net resistance with 
the earth upon the heel of the wall is greater than with an equal 
depth of water, it will be assumed that the water extends to the 
bottom of the wall. 

If the water finds its way under and around the foundation of 
the wall, even in very thin sheets, it will decrease the pressure of 
the wall on the foundation, and, consequently, decrease the 
stability of the wall. The effective weight of the submerged por¬ 
tion'of the wall will be decreased 62 J- lbs. per cu. ft. However, the 
assumption that water in hydrostatic condition finds its way under 
or into a dam is hardly admissible; hence the effect of buoyancy 
will not be considered.* 

489. Co-efficient of Friction. The values of the co-efficient of 
friction most frequently required in masonry computations are given 
in the table on page 315. There will be frequent reference to this 
table in subsequent chapters ; and therefore it is made more full 
than is required in this connection. The values have been collected 
from the best authorities, and are believed to be fair averages. See 
also the table on page 276. 

490. Condition for Equilibrium. In order that the wall may 

not slide, it is necessary that the product found by multiplying the 
co-efficient of friction by the sum of the weight of the wall and the 
vertical pressure of the water shall be greater than the horizontal 
pressure of the water. That is to say, in order that the dam may 
not slide it is necessary that pi ( W -j- 31.25 Id F) shall be greater 
than H ; or, in mathematical language, 

^ H ^ 31.25 F 

M > W + 31.25 F b f> w(ht+i F V + \ F \) + 31.25 F F 9 


* Since the above was written, Jas. B. Francis presented a paper (May 16, 1888) 
before the American Society of Civil Engineers, which seems to show that water 
pressure is communicated, almost undiminished, through a layer of Portland cement 
mortar (1 part cement and 2 parts sand) 1 foot thick. 







STABILITY OF GRAVITY DAMS. 


315 


ART. 1.] 


TABLE 36. 

Co efficients of Friction for Dry Masonry. 


Description of the Masonry. 


Co-efficient. 


Soft limestone on soft limestone, both well dressed. 

Brick-work on brick-work, with slightly damp mortar. 

Hard brick-work on hard brick-work, with slightly damp mortar. 

Point-dressed granite on like granite... 

“ “ “ “ well-dressed granite. 

Common brick on common brick.„. 

“ “ “ hard limestone. 

Hard limestone on hard limestone, with moist mortar. 

Bet.on blocks (pressed) on like beton blocks. 

Fine-cut granite on pressed “ “ . 

Well-dressed granite on well dressed granite. 

Polished limestone on polished limestone. . 

Well-dressed granite on like granite, with fresh mortar. 

Common brick on common brick, with wet mortar. 

Polished marble on common brick. 


0.75 

0.75 

0.70 

0.70 

0.65 

0.65 

0.65 

0.65 

0.65 

0.60 

0.60 

0.60 

0.50 

0.50 

0.45 


Point-dressed granite on gravel. 

“ “ “ “ dry clay.. 

“ “ “ “ sand. 

*• “ “ “ moist clay. 

Wrought iron on well-dressed limestone. 

“ “ “ hard, well dressed limestone, wet 

Oak, flatwise, on limestone. 

“ endwise, on limestone. 


0.60 

0.50 

0.40 

0.33 

0.50 

0.25 

0.65 

0.40 


which reduced becomes 

62.5 h /4Y 

^ > w (2 t + h (b' + *,)) + 63.5 h b'' ' ' ' w 

The weight of a cubic foot of masonry, w, varies between 125 lbs. 
for concrete or poor brick-work, and 160 lbs. for granite ashlar. 
Dams are usually built of rubble, which weighs about 150 lbs. per 
cu. ft. To simplify the formula, we will assume that the masonry 
weighs 125 lbs. per cu. ft.; i. e., that the weight of a cubic foot of 
masonry is twice that of water. This assumption is on the safe side, 
whatever the kind of masonry.* Making this substitution in (4) 


* Increased safety generally requires increased cost of construction, and hence 
it is not permissible to use approximate data simply because the error is on the side 
toward safety. It will be shown that there is no probability of anj dam s failing b} 
sliding, and that the size, and consequently the volume and cost, are determined by 




































316 


MASONRY DAMS. 


[CHAP. XIII. 


gives 


M > °' 5 2 t + h (2 V + b ,)' 



Other things being the same, the thinner the wall at the top, 
the easier it will slide. If the section of the wall is a triangle, i. e., 
if t = 0, then by equation (5) we see that the dam is safe against 
sliding when 


M > 0-5 


1 

(**' + *,) 



An examination of the table on page 315 shows that there is no 
probability that the co-efficient of friction will be less than 0.5; and 
inserting this value of yu in (6) shows that sliding can not take 
place if (2 V -f &,) > or = 1. To prevent overturning, (b f + bj 
is usually = or > 1 (see Fig. 72, page 328); and, besides, a con¬ 
siderable thickness at the top (see § 509) is needed to resist the 
shock of waves, etc. Hence there is no probability of the dam’s 
failing by sliding forward. Further, the co-efficient of friction in 
the table on page 315 takes no account of the cohesion of the mor¬ 
tar, which may have a possible maximum value, for best Portland 
mortar, of 36 tons per sq. ft. (500 lbs. per sq. in.); and this gives 
still greater security. Again, the earth on, and also in front of, the 
toe of the wall adds greatly to the resistance against sliding. Fi¬ 
nally, it is customary to build masonry dams of uncoursed rubble 
(§§ 213-17), to prevent the bed-joints from becoming channels for 
the leakage of water; and hence the stones are thoroughly inter¬ 
locked,—which adds still further resistance. Therefore it is certain 
that there is no danger of any masonry dam’s failing by sliding for¬ 
ward under the pressure of still water. 

491. It has occasionally happened that dams and retaining walls 
have been moved bodily forward, sliding on their base; but such an 
occurrence is certainly unusual, and is probably the result of the 
wall’s having been founded on an unstable material, perhaps on an 
inclined bed of moist and uncertain soil. In most that was said in 
Part III concerning foundations, it was assumed that the founda- 


t he dimensions required to prevent crushing and overturning; hence this approxima¬ 
tion involves no increase in the cost. 


I 








ART. 1.] 


STABILITY OF GRAVITY DAMS. 


31? 


tion was required to support only a vertical load. When the struct- 
ure is subjected also to a lateral pressure, as in dams, additional 
means of security are demanded to prevent lateral yielding. 

When the foundation rests upon piles a simple expedient is to 
drive piles in front of and against the edge of the bed of the founda¬ 
tion; but obviously this is not of much value except when the piles 
reach a firmer soil than that on which s the foundation directly rests. 
If the piles reach a firm subsoil, it will help matters a little if the 
upper and more yielding soil is removed from around the top of the 
pile, and the place filled with broken stone, etc. Or a wall of piles 
may be driven around the foundation at some distance from it, and 
timber braces or horizontal buttresses of masonry may be placed at 
intervals from the foundation to the piles. A low masonry wall is 
sometimes used, instead of the wall of piles, and connected with the 
foot of the main wall by horizontal buttresses, whose feet, on the 
counter-wall, are connected by arches in a horizontal plane in order 
to distribute the pressure more evenly. 

In founding a dam upon bed-rock, the resistance to sliding on 
the foundation may be greatly increased by leaving the bed rough ; 
and, in case the rock quarries out with smooth surfaces, one or more 
longitudinal trenches may be excavated in the bed of the foundation, 
and afterwards be filled with the masonry. 

In the proposed Quaker Bridge dam the maximum horizontal 
thrust of the water is equal to 0.597 of the weight of the masonry. 

492. Stability against Overturning. The horizontal pres¬ 
sure of the water tends to tip the wall forward about the front of 
any joint, and is resisted by the moment of the weight of the wall. 
For the present, it will be assumed that the wall rests upon a rigid 
base, and therefore can fail only by overturning as a whole. 

The conditions necessary for stability against overturning can be 
completely determined either by considering the moments of the 
several forces, or by the principle of resolution of forces. In the 
following discussion the conditions will be first determined by mo¬ 
ments, and afterward by resolution of forces. 

493. A. By Moments. The Overturning Moment. The pressure 
of the water is perpendicular to the pressed surface. If the water 
presses against an inclined face, then the pressure makes the same 
angle with the horizontal that the surface does with the vertical. 
Since there is a little difficulty in finding the arm of this force, it is 




318 


MASONRY DAMS. 


[CHAP. XIIL 


more convenient to deal with the horizontal and vertical components 
of the pressure. 

The horizontal pressure of the water can be found by equation 
(i), page 313. The arm of this force is equal to ^ h (principle 3, 
§ 481). Hence the moment tending to overturn the wall is equal to 


4 Hh = 4 31.25 h 3 = 10.42 E, 


(-) 


which, for convenience, represent by M x . 

494. The Resisting Moments. The forces resisting the over¬ 
turning are ( 1 ) the weight of the wall and ( 2 ) the vertical pressure 
of the water on the inclined face. 

The weight of the wall can be computed by equation (3), page 
313. It acts vertically through the center of gravity of the cross 
section. 

The center of gravity can he found algebraically or graphically. 

There are several ways in each case, hut 
the following graphical solution is the sim¬ 
plest. In Fig. G9, draw the diagonals D B 
and A E, and lay off A J = E I ; then 
draw D J, and mark the middle of it Q. 
The center of gravity, 0, of the area 
ABED is at a distance from Q towards 
B equal to J Q B. This method is appli¬ 
cable to any four-sided figure. 

The position of the center of gravity can 
also be found algebraically by the principle 
that the moment of the entire mass about 
any point, as A, is equal to the moment of the part A D G, plus 
che moment of the portion D E F G, plus the moment of the part 
E B F ,—all about the same point, A. Stating this principle alge¬ 
braically gives 



f ^ (i ^i) + GM + A &i) + £ E V h E -}- t -j- h 

— E E -f- h t -j- y E Z>,) Xy . . • . 

in which x = the distance A C. Solving (8) gives 

— ^ E -j— ^ E b n -j- h tb l -j- -£■ t* -J -Af h t E -j- E E b y 

i h (V + b ) + l ' • 


( 8 ) 


( 9 ) 
















ART. 1.] 


STABILITY OF GRAVITY DAMS. 


319 


The arm of the weight is A C (= x), and therefore the mo¬ 
ment is 

WxAC=w[ht + iF(F + l> 1 )]x,. . . (10) 

which, for convenience, represent by Jf 2 . 

495. The vertical pressure of the water on the inclined face, 
E B, has been computed in § 487, which see. This force acts ver¬ 
tically between Band B, at a distance from B equal to \ F B\ the 
arm of this force is A B — -J- F B = l — UV = h b x + t + § lib'. 
Therefore, the moment of the vertical pressure on the inclined 
face is 

31.25 F V (h l x + t + f h V), .... (11) 

which, for convenience, represent by M % . Of course, if the pressed 
face is vertical, M % will be equal to zero. 

496. The moment to resist overturning is equal to the sum of 
(10) and (11) above, or d/ 2 + M z . 

The moment represented by the sum of M 2 and M % can be deter¬ 
mined directly by considering the pressure of the water as acting 
perpendicular to E B at ^ E B from B ; the arm of this force is a 
line from A perpendicular to the line of action of the pressure. If 
the cross section were known, it would be an easy matter to measure 
this arm on a diagram; but, in designing a dam, it is necessary to 
know the conditions requisite for stability before the cross section 
can be determined, and hence the above method of solution is the 
better. 

497. Condition for Equilibrium. In order that the wall may 
not turn about the front edge of a joint, it is necessary that the 
overturning moment, M x , as found by equation (7), shall be less 
than the sum of the resisting moments, J/ 2 and M % , as found by 
equations (10) and (11); or, in other words, the factor against over- 

turning = ^* ■■ 4 — .(12) 

498. Factor of Safety against Overturning. In computing the 
stability against overturning, the vertical pressure of the water 
against the inside face is frequently neglected; i. e ., it is assumed 
that M s , as above, is zero. This assumption is always on the safe 
side. Computed in this way, the factor of safety against overturn¬ 
ing for the proposed Quaker Bridge dam, which when completed 






320 


MASONRY DAMS 


[CHAP. XIII. 


will be considerably the largest dam in the world, varies between 
2.07 and 3.68. Krantz,* who included the vertical component in 
his computations, considers a factor of 2.5 to 5.55 as safe, the larger 
value being for the largest dam, owing to the more serious conse¬ 
quences of failure. The greater the factor of safety provided for, 
the greater is the first cost; and the less the factor of safety, the 
greater the expense of maintenance, including a possible reconstruc¬ 
tion of the structure. 

499. B. By Resolution of Forces. In Fig. 70, K is the center 

of pressure of the water on the back of 
the wall. K B — \ E B. o is the center 
of gravity of the wall,—found as already 
described. Through K draw a line, Ka , 
perpendicular to E B; through o draw a 
vertical line o a. To any convenient 
scale lay off ab equal to the total pressure 
of the water against E B, and to the 
same scale make af equal to the weight 
of an elementary section of the wall. 
Complete the parallelogram ab ef. The 
diagonal ae intersects the base of the 



Fig. 70. 


wall at N. 

500. On the assumption that the masonry and foundation 
are absolutely incompressible (the compressibility will be considered 
presently), it is clear that the wall will not overturn as long as the 
resultant ae intersects the base AB between A and B. The factor 

A C 

against overturning is which is the equivalent of equation (12). 


The wall can not slide horizontally on the base, when the angle 
NaC is less than the angle of repose, i. e., when tan .2^(7 is less 
than the co-efficient of friction. The factor against sliding is equal 
to the % co-efficient of friction divided by tan .NaC, which is only 
another way of stating the conclusion drawn from equation (4), 
page 315. 

501. Stability against Crushing. The preceding discussion 
of the stability against overturning is on the assumption that the 
masonry does not crush. This method of failure will now be con- 


* “ Study of Reservoir Walls,” Mahan’s translation, p. 53. 
















ART. 1.] 


STABILITY OF GRAVITY DAMS. 


321 


sidered. When the reservoir is empty, the pressure tending to 
produce crushing is the weight of the dam alone, which pressure is 
distributed uniformly over the horizontal area of the wall. When 
the reservoir is full, the thrust of the water modifies the distribution 
of the pressure, increasing the pressure at the front of the wall and 
decreasing it at the back. We will now determine the law of the 
variation of the pressure. 

Let A B, Fig. 71, represent the base of a vertical section of the 
dam; or A B may represent the rect¬ 
angular base (whose width is a unit) of 
any two bodies which are pressed against 
each other by any forces whatever. 

M — the resulting moment (about A) of 
all the external forces. In the 
case of a dam, M — M 1 — M z ,—see 
equations (7) and (11). 

W = the total normal pressure on A B. 

In the case of a dam, W — the weight of the masonry. 

P — the maximum pressure, per unit of area, at A. 
p = the change in unit pressure, per unit of distance, from A 
towards B. 

x = any distance from A towards B. 
p — p x — the pressure per unit at a distance x from A. 

Y — a general expression for a vertical force. 



The remainder of the nomenclature is as in § 484, page 312. 
Taking moments about A gives 

M— Wx-p (P-px) dx. x = 0; * . . (13) 

% 

M- Wx + iPV -ipl 3 = 0. ..... (14) 

For equilibrium, the sum of the forces normal to A B must also 
be equal to zero ; or 

2Y=-W- f f l {P — px)dx = 0, . . . (15) 

t'Q 

from which 

p r = 2 P l - 2 W. . . . . . . (16) 






322 


MASONRY DAMS. 


[CHAP. XIII, 


502. Maximum Pressure. Combining (16) with (14) and re 

during, 

4 W 6 W~x . 6 M 


P =-—— 

i r 


+ p ■ ■ 


(17) 


tf the stability against overturning be determined algebraically, i. e., 
by equation (12), then M and x are known, and P can be computed 
by equation (17). 

If the wall is symmetrical x — \ l, and (17) becomes 


P = 


W 6 M 
T ' r : 



Equation (18) is a more general form of equation (1), page 205, 
since in the latter there is but one external force acting, and that 
is horizontal. 


W . 


In equation (18), notice that — is the uniform pressure on A B 

t 

6 M 

due to the weight of the wall; also that is the increase of pres- 

c 


sure at A due to the tendency to overturn, and that consequently 
the uniform pressure at B is decreased a like amount. 

503. The maximum pressure may be found also in another way. 
Assume that N , Fig. 71, is the center of pressure. Let p 1 ( = B L) 
represent the pressure at B, and p 9 (= A K) that at A ; and any 
intermediate ordinate of the trapezoid A B L K will represent the 
pressure at the corresponding point. Then, since the forces acting 
on A B must be in equilibrium for translation, the area of the 
trapezoid will represent the entire pressure on the base A B. Stated 
algebraically, this is 

1 = w - .(i9) 


Also, since the forces acting on A B must be in equilibrium for 
rotation, the moment of the pressure to the right of JV must be 
equal to that to the left; that is to say, the center of gravity of the 
trapezoid ABLE must lie in the line N J. By the principles of 
analytical mechanics, the ordinate A E to the center of gravity 
ABLE is 



v P, + Pi) 


( 20 ) 














AKT. 1.] 


STABILITY OF GKAVITY DAMS. 


323 


Solving (19) and (20) gives 


P* = 


4 IF 6 Wx 


l 


r 


( 21 ) 


If the wall is a right-angled triangle with the right angle at A, 
x = i l, which, substituted in the above expression, shows that the 

2 IF 

pressure at A is —-—, and also that the pressure at B is zero,—all 


of which is as it should be. Equation (21) is a perfectly general 
expression for the pressure between any two plane surfaces pressed 
together by normal forces. Notice that equation (21) is identical 
with the first two terms of the right-hand side of equation (17). 

The form of (21) can be changed by substituting for x its value 


$1 — d\ then 


TF , 6 Wd 
~ i + r ‘ 


( 22 ) 


Equation (22) gives the pressure at A due to the weight of the 
wall; but it will also give the maximum pressure on the base due 
to both the vertical and the horizontal forces, provided d be taken 
as the distance from the middle of the base to the point in which 
the resultant of all the forces cuts the base. Therefore we may 
write 

IF 6 Wd 
i + r ' 



504. Equation (23) is the equivalent of equation (17), page 322. 
It is well to notice that equation (23) is limited to rectangular hori¬ 
zontal cross-sections, since it was assumed that the pressure on the 
section varies as the distance back from the toe. If the stability 
against overturning is determined algebraically, as by equation (12), 
then equation (17) is the more convenient; but if the stability is 
determined graphically, as in Eig. 70, then equation (22) is the 


simpler. 


Notice that if d = \ l, P — 


2 IF 
l 9 


which is in accordance 


with what is known in the theory of arches as the principle of the 
middle third ; that is, as long as the center of pressure lies within 
the middle third of the joint, the maximum pressure is not more 
than twice the mean, and there is no tension in any part of the 
joint. 















324 


MASONRY DAMS. 


[CHAP. XIII. 


W 

Notice, in equation (23), that -=- is the uniform load on the base; 

i 

6 Wd 

is the increase of pressure due to the eccentric¬ 


and also that 


r 


ity of the load. It is immaterial whether the deviation d is caused 
by the form of the wall or by forces tending to jn-oduce overturn¬ 
ing. 

505. Tension on the Masonry. By an analysis similar to that 
above, it can be shown that the decrease in pressure at B, due to 
the overturning moment, is equal to the increase at A. If d = } l, 
then by equation (23) the increase at A and decrease at B is W, 
that is to say, the pressure at A is 2 W and that at B is zero. 
Therefore, if the center of pressure departs more than 1 1 from the 
center of the base, there will be a minus pressure, i. e. tension, at 
B. Under this condition, the triangle A VK' , in Fig. 71, page 
321, represents the total pressure, and the triangle i? V If the total 
tension on the masonry ,—A K' being the maximum pressure at A , 
and B L f the maximum tension at B. 

If a good quality of cement mortar is used, it is not unreason¬ 
able to count upon a little resistance from tension. As a general 
rule, it is more economical to increase the quantity of stone than the 
quality of the mortar ; but in dams it is necessary to use a good 
mortar to prevent (1) leakage, (2) disintegration on the water side, 
and (3) crushing. If the resistance due to tension is not included 
in the computation, it is an increment to the computed margin of 
safety. 

506. If the masonry be considered as incapable of resisting by 
tension, then when d in equation (23) exceeds i l the total pres¬ 
sure will be borne on A V, Fig. 71. In this case A N' (the distance 
from A to the point where the resultant pierces the base) will be 
less than -J- l. If A K" represents the maximum pressure P, then 
the area of the triangle A VK " will represent the total weight IF. 
The area of A V K" = £ A K" X A V = { P X 3 A If'. Hence 
l P X 3 A N’ = IF, or 


2 IF 2 IF 

3 A N' ~~ 3 1 — d)' 


(24) 


To illustrate the difference between equations (23) and (24), 







ART. 1.] 


STABILITY OF GRAVITY DAMS. 


325 


assume that the distance from the resultant to the center of the base 
is one quarter of the length of the base, i. e., assume that d = il. 
Then, by equation (23), the maximum pressure at A is 


W , 6 Wl _ 01 W 

l A- r4 -- 2 x > 


and by equation (24) it is 


_ » W _ W 

3 l ' 


. . (25) 


(26) 


That is to say, if the masonry is capable of resisting tension, equa¬ 
tion (25) shows that the maximum pressure is 2£ times the pressure 
due to the weight alone ; and if the masonry is incapable of resist¬ 
ing tension, equation (26) shows that the maximum pressure is 2f 
times the pressure due to the weight alone. 

Notice that equation (24) is not applicable when d is less than 

; in that case, equation (23) must be used. 

507. Limiting Pressure. As a preliminary to the actual design¬ 
ing of the section, it is necessary to fix upon the maximum pressure 
per square foot to which it is proposed to subject the masonry. Of 
course, the allowable pressure depends upon the quality of the 
masonry, and also upon the conditions assumed in making the com¬ 
putations. It appears to be the custom, in practical computations, 
to neglect the vertical pressure on the inside face of the dam, i. e ., 
to assume that d/ 3 , equation (11), page 319, is zero ; this assumption 
is always on the safe side, and makes the maximum pressure on the 
outside toe appear greater than it really is. Computed in this way, 
the maximum pressure on rubble masonry in cement mortar in 
some of the great dams of the world is from 11 to 14 tons per sq. 
ft. The proposed Quaker Bridge dam is designed for a maximum 
pressure of 16.6 tons per sq. ft. on massive rubble in Portland 
cement mortar. 

For data on the strength of stone and brick masonry, see §§ 
221-23 and §§ 246-48, respectively. 

508. The actual pressure at the toe will probably be less than 
that computed as above. It was assumed that the weight of the 
wall was uniformly distributed over the base ; but if the batter is 
considerable, it is probable that the pressure due to the weight of 
the wall will not vary uniformly from one side of the base to tho 








I 


326 


MASONRY DAMS. 


[CHAP. XIII- 


other, but will be greater on the central portions. The actual 
maximum will, therefore, probably occur at some distance back 
from the toe. Neither the actual maximum nor the point at which 
it occurs can be determined. 

Professor Rankine claims that the limiting pressure for the out¬ 
side toe should be less than for the inside toe. Notice that the 
preceding method determines the maximum vertical pressure. 
When the maximum pressure on the inside toe occurs, the only 
force acting is the vertical pressure ; but when the maximum on 
the outside occurs, the thrust of the water also is actiug, and there¬ 
fore the actual pressure is the resultant of the two. With the pres¬ 
ent state of our knowledge, we can not determine the effect of a 
horizontal component upon the vertical resistance of a block of stone, 
but it must weaken it somewhat. 


Art. 2. Outlines of the Design. 

509. Width on Top. As far as the forces already considered 
are concerned, the width of the wall at the top might be nothing, 
since at this point there is neither a pressure of water nor any 
weight of masonry. But in practice we must consider the shock of 
waves and ice, which in certain cases may acquire great force and 
prove very destructive to the upper portion of the dam. This force 
can not be computed, and hence the width on top must be assumed. 
This width depends to a certain extent upon the height and length 
of the dam. The top of large dams may be used as a roadway. 
Krantz * says that it is “scarcely possible to reduce the top width 
below 2 metres (6.5 ft.) for small ponds, nor necessary to make it 
more than 5 metres (16.4 ft.) for the largest.” 

Fig. 72, page 328, gives the width on top of Krantz’s profile type, 
and also of the profile recommended by the engineers of the 
Aqueduct Commission for the proposed Quaker Bridge dam. 

510. The Profile. In designing the vertical cross section of a 
gravity dam to resist still water, it is necessary to fulfill three con¬ 
ditions : (1) To prevent sliding forward, equation (4), page 315, 
must be satisfied; (2) to resist overturning, equation (12), page 319, 
must be satisfied ; and (3) to resist crushing, equation (23), page 
323, or (24), page 324, must be satisfied. As these equations really 


* “ Study of Reservoir Walls,” Malian’s translation, p. 35. 





AET. 2.] 


OUTLINES OF THE DESIGN. 


327 


involve only three variables, viz.: h, 1 ) x , and V ,—the height of the 
dam and the batter of the two faces,—they can be satisfied exactly. 
It has been shown that there is no danger of the dam’s sliding for¬ 
ward even if the width on top is zero ; and hence there are practi¬ 
cally but two conditions to be fulfilled and two variables to be 
determined. To prevent overturning when the reservoir is full, 
equation (12) must be satisfied ; and to prevent crushing, equation 
(23)—or (24)—must be satisfied for the point A (Figs. G9, 70, etc.) 
when the reservoir is full, and for B when the reservoir is empty. 

Although it is possible to satisfy these conditions exactly, the 
theoretical profile can be obtained only by successive approxima¬ 
tions. This is done by dividing the profile into elementary hori¬ 
zontal layers, beginning at the top, and determining the dimension 
of the base of each layer separately. The theoretical width at the 
top being zero and the actual width being considerable, a portion of 
the section at the top of the dam will be rectangular. A layer being 
given, and the profile of the portion above it being known, certain 
dimensions are assumed for the lower base of the layer; and the 
stability against overturning is then determined by applying equa¬ 
tion (12), or by the method of Fig. 70 (page 320). The maximum 
pressure at A is then found by applying equation (17) or (23), after 
which the maximum pressure at B when the reservoir is empty 
must be determined by applying equation (23). If the first dimen¬ 
sions do not give results in accordance with the limiting conditions, 
others must be assumed and the computations repeated. A third 
approximation will probably rarely be needed. 

It is not necessary to attempt to satisfy these equations precisely, 
since there are a number of unknown and unknowable factors, as the 
weight of the stone, the quality of the mortar, the character 
of the foundation, the quality of the masonry, the hydrostatic 
pressure under the mass, the amount of elastic yielding, the 
force of the waves and of the ice, etc., which have more to do 
with the ultimate stability of a dam than the mathematically exact 
profile. It is therefore sufficient to assume a trial profile, being 
guided in this by the matters referred to in § 511 and § 512, and 
test it at a few points by applying the preceding equations ; a few 
modifications to more nearly satisfy the mathematical conditions cr 
to simplify the profile is as far as it is wise to carry the theoretical 
determination of the profile. 





328 


MASONKY DAMS. 


[CHAP. XIII. 


511. Krantz’s Study of Keservoir "Walls, translated from the 
French by Capt. F. A. Mahan, U. S. A., gives the theoretical pro¬ 
files for dams from 1G.40 ft. (5 metres) to 164 ft. (50 metres) high. 
The faces are arcs of circles. The mathematical work of determin¬ 
ing the profiles is not given ; but it is evident that the polygonal 
profile was deduced as above described, and that an arc of a circle 
was then drawn to average the irregularities. The largest of these 
profiles is shown in Fig. 72 by the broken line. The others are 
simply the upper portion of the largest, with the thickness and the 
height of the portion above the water decreased somewhat and the 
radius of the faces modified correspondingly. 



The larger profile of Fig. 72 is that recommended by the engi¬ 
neers of the Aqueduct Commission for the proposed Quaker Bridge 
dam. The profiles of most of the high masonry dams of the world 






















ART. 2.] 


OUTLINES OF THE DESIGN. 


329 


are exceedingly extravagant, and hence it is not worth while to give 
examples. 

512. Prof. Wm. Cain has shown * that the equations of condi¬ 
tion are nearly satisfied by a cross section composed of two tra¬ 
pezoids, the lower and larger of which is the lower part of a triangle 
having its base on the foundation of the dam and its apex at the 
surface of the water, and the upper trapezoid having for its top the 
predetermined width of the dam on top (§ 509), and for its sides 
nearly vertical lines which intersect the sides of the lower trapezoid. 
The width of the dam at the bottom is obtained by applying the 
equations of condition as above. The relative batter of the up¬ 
stream and down-stream faces depends upon the relative factors 
of safety for crushing and overturning. This section gives a 
factor of safety which increases from bottom to top,—an important 
feature. 

513. The Plan. If the wall is to be one side of a rectangular 
reservoir, all the vertical sections will be alike ; and therefore the 
heel, the toe, and the crest will all be straight. If the wall is to be 
a dam across a narrow valley, the height of the masonry, and conse¬ 
quently its thickness at the bottom, will be greater at the center 
than at the sides. In this case the several vertical cross sections 
may be placed so that (1) the crest will be straight, or (2) so that 
the heel will be straight in plan, or (3) so that the toe will be 
straight in plan. Since the up-stream face of .the theoretical pro¬ 
file is nearly vertical (see Fig. 72), there will be very little difference 
in the form of the dam whether the several cross sections are 
placed in the first or the second position as above. If the crest is 
straight, the heel, in plan, will be nearly so ; if the crest is straight, 
the toe, in plan, will be the arc of a circle such that N the middle 
ordinate to a chord equal to the span (length of the crest) will be 
equal to the maximum thickness of the dam ; and if the toe is 
made straight, the crest will become a circle of the same radius. 
This shows that strictly speaking it is impossible to have a straight 
gravity dam across a valley, since either the crest or toe must be 
curved. The question then arises as to the relative merits of these 
two forms. 

514. Straight Crest vs. Straight Toe. The amount of masonry 


* Engineering News , vol. xix. pp. 512-13. 






330 


MASONRY DAMS. 


[CHAP. XIII. 


I 


in the two forms is the same, since the vertical sections at all points 
are alike in both.* 

The stability of the two forms, considered only as gravity dams, 
is the same, since the cross sections at like distances from the center 
are the same. 

The form with a curved crest and straight toe will have a slight 
advantage due to its possible action as an arch. However, it is not 
necessary to discuss further the relative advantages of these two 
types, since it will presently be shown that both the toe and the crest 
of a gravity dam should be curved. 

515. Gravity vs. Arch Dams. A dam of the pure gravity type 
is one in which the sole reliance for stability is the weight of the 
masonry. A dam of the pure arch type is one relying solely upon 
the arched form for stability. With the arched dam, the pressure 
of the water is transmitted laterally through the horizontal sections 
to the abutments (side hills). The thickness of the masonry is so 
small that the resultant of the horizontal pressure of the water and 
the weight of the masonry passes outside of the toe ; and hence, 
considered only as a gravity dam, is in a state of unstable equilib¬ 
rium. If such a dam fails, it will probably be by the crushing 
of the masonry at the ends of the horizontal arches. In the 
present state of our knowledge concerning the elastic yielding of 
masonry, we can not determine, with any considerable degree of 
accuracy, the distribution of the pressure over the cross section of 
the arch (see Art. 1, Chap. XVIII). 

If it were not for the incompleteness of our knowledge of the 
laws governing the stability of masonry arches, the arch dam would 
doubtless be the best type form, since it requires less masonry for 
any particular case than the pure gravity form. The best infor¬ 
mation we have in regard to the stability of masonry arches is de¬ 
rived from experience. The largest vertical masonry arch in the 
world has a span of only 220 feet. There are but two dams of the 
pure arch type in the world, viz.: the Zola f in France and the 

* If the valley across which the dam is built has any considerable longitudinal slope, 
as it usually will have, there will be a slight difference according to the relative posi¬ 
tion of the two forms. If two ends remain at the same place, the straight toe throws 
the dam farther up the valley, makes the base higher, and consequently slightly de- 
•creases the amount of masonry. 

t For description, see Report on Quaker Bridge Dam, Engineering News , vol. xix. 
p. 6 et seq. 








ART. 2.] 


OUTLINES OF THE DESIGN. 


331 


Bear Valley* in Southern California. The length of the former is 
205 feet on top, height 122 feet, and radius 158 feet; the length 
of the latter is 230 feet on top, height 64 feet, radius of top 
335 feet and of the bottom 226 feet. The experience with large 
arches is so limited (see Table 63, page 502), as to render it un¬ 
wise to make the stability of a dam depend wholly upon its action 
as an arch, except under the most favorable conditions as to rigid 
side-hills and also under the most unfavorable conditions as to cost 
of masonry. Notice that with a dam of the pure arch type, the 
failure of one part is liable to cause the failure of the whole ; while 
with a gravity section, there is much less danger of this. Further, 
since the average pressure on the end arch stones increases with the 
span, the arch form is most suitable for short dams. 

516. Curved Gravity Dams. Although it is not generally wise 
to make the stability of a dam depend entirely upon its action as 
an arch, a gravity dam should be built in the form of an arch, i. e ., 
with both crest and toe curved, and thus secure some of the advan¬ 
tages of the arch type. The vertical cross section should be so pro¬ 
portioned as to resist the water pressure by the weight of the 
masonry alone, and then any arch-like action will give an addi¬ 
tional margin for safety. If the section is proportioned to resist 
by its weight alone, arch action can take place only by the elastic 
yielding of the masonry under the water pressure ; but it is known 
that masonry will yield somewhat, and that therefore there will be 
some arch action in a curved gravity dam. Since but little is known 
about the elasticity of stone, brick, and mortar (see § 16), and noth¬ 
ing at all about the elasticity of actual masonry, it is impossible 
to determine the amount of arch action, i. e., the amount of pres¬ 
sure that is transmitted laterally to the abutments (side-hills). 

That it is possible for a dam to act as an arch and a gravity dam 
at the same time is shown as follows : “ Conceive a dam of the 
pure arch type, of thin rectangular cross section so as to have no 
appreciable gravity stability. Conceive the dam to be made up of 
successive horizontal arches with key-stones vertically over each 
other. The thrust in each arch will increase with the depth, but 
the spans will, under the ordinary practical conditions, decrease 
with the depth, so that the tendency to Settle at the crown 9 (move 
horizontally) will be approximately equal in each. If now we adopt 


* For destription, see Engineering News , vol. xix. pp. 513-15. 







332 


MASONRY DAMS. 


[CHAP. xiir.. 


a triangular in place of a rectangular cross section, we increase the 
areas and decrease the unit pressures from arch-thrust as we go 
down, and hence decrease compression and consequent horizontal 
f settlement 9 of the arches ; in other words, we introduce a tendency 
in the water face of the dam to rotate about its lower edge. But 
this is precisely the tendency which results from the elastic action 
of the mass in respect to gravity stability, which latter we have at 
the same time introduced by adopting the gravity section. Hence 
the two act in perfect harmony, and. there will be a certain size of 
triangular section (theoretically,—practically it could not be exact) 
at which precisely half the stability will be due to arch action and 
half to gravity action, each acting without any appreciable conflict 
or interference with the other/'* 

517. In addition to the increased stability of a curved gravity 
dam due to arch action, the curved form has another advantage. 
The pressure of the water on the back of the arch is everywhere 
perpendicular to the up-stream face, and can be decomposed into 
two components—one perpendicular to the chord (the span) of the 
arch, and the other parallel to the chord of the arc. The first 
component is resisted by the gravity and arch stability of the dam, 
and the second throws the entire up-stream face into compression. 
The aggregate of this lateral pressure is equal to the water pressure 
on the projection of the up-stream face on a vertical plane perpen¬ 
dicular to the span of the dam. This pressure has a tendency to 
close all vertical cracks and to consolidate the masonry transversely, 
—which effect is very desirable, as the vertical joints are always less 
perfectly filled than the horizontal ones. This pressure also pre¬ 
pares the dam to act as an arch earlier than it would otherwise do, 
and hence makes available a larger amount of stability due to arch 
action. 

The compression due to these lateral components is entirely in¬ 
dependent of the arch action of the dam, since the arch action 
would take place if the pressure on the dam were everywhere per¬ 
pendicular to the chord of the arch. Further, it in no way weakens 
the dam, since considered as a gravity dam the effeci of the thrust 
of the water is to relieve the pressure on the bach face, and con' 
sidered as an arch the maximum pressure occurs at the sides of the 
vdown-stream face. 


* Editorial in Engineering News, vol. xix. p. 272. 









art. 2.] 


OUTLINES OF THE DESIGN. 


333 


The curved dam is a little longer than a straight one, and hence 
would cost a little more. The difference in length between a chord 
and its arc is given, to a close degree of approximation, by the formula 



in which a — the length of the arc, c = the length of the chord, 
and r = the radius. This shows that the increase in length due to 
the arched form is comparatively slight. For example, if the chord 
is equal to the radius, the arch is only or 4 per cent., longer than, 
the chord. Furthermore, the additional cost is less, proportionally, 
than the additional quantity of masonry ; for example, 10 per cent, 
additional masonry will add less than 10 per cent, to the cost. 

518. Of the twenty-five most important masonry dams in the 
world, two are of the pure arch type, fifteen are of the curved 
gravity type, and eight are of the straight gravity type. The eight 
highest clams are of the curved gravity type.* 

519. Quality of the Masonry. It is a well settled principle 
that any masonry structure which sustains a vertical load should 
have no continuous vertical joints. Dams support both a horizontal 
and a vertical pressure, and hence neither the vertical nor the hori¬ 
zontal joints should be continuous. This requires that the masonry 
shall be broken ashlar (Fig. 39, page 136) or random squared-stone 
masonry (Fig. 44, page 137), or uncoursed rubble (Fig. 45, page 137). 
The last is generally employed, particularly for large dams. The 
joints on the faces should be as thin as possible, to diminish the 
effect of the weather on the mortar and also the cost of repointing. 
In ordinary walls much more care is given to filling completely 
the horizontal than the vertical ones ; but in dams and reservoir 
walls it is important that the vertical joints also shall be completely 
filled. 

To prevent leakage, it is very important that all spaces between 
the stones should be filled completely with good mortar, or better, 
with mortar impervious to water (see § 141). If the stone itself is 
not impervious, the wall may be made water tight by the ap¬ 
plication of Sylvester's washes (§ 263) to the inside face of the 


dam 


* For source of information concerning these dams, see § 520—Bibliography of 
Masonry Dams. 









334 


MASONRY DAMS. 


[CHAP. XIIR 


520 . Bibliography of Masonry Dams. Design and Construc¬ 
tion of Masonry Dams, Rankin e, (Miscellaneous Scientific Papers, 
pp. 550-61.) Study of Reservoir Walls , Krantz, (translated from 
the French by Capt. F. A. Mahan, U. S. A.) Profiles of High 
Masonry Dams , McMaster, (published in Van Nostrand’s Engineer¬ 
ing Magazine and also as No. 6 of Van Nostrand’s Science Series.) 
Strains in High Masonry Dams, E. Sherman Gould, (Van 
Nostrand’s Engineering Magazine, vol. 30, p. 265 et seq.). Histori¬ 
cal and Descriptive Revieiv of Earth and Masonry Dams, with 
Plans, David Gravel, (Scientific American Supplement, No. 595 
(May 28, 1887), pp. 9496-9500.) Wegmann’s Design and Con¬ 
struction of Masonry Dams gives an account of methods em¬ 
ployed in determining the profile of the proposed Quaker Bridge 
dam, and also contains illustrations of the high masonry dams 
of the world. For a general discussion of high masonry dams, 
including a consideration of the best form for the horizontal 
cross section, a full description of the proposed Quaker Bridge 
dam and a comparison of it with other great dams, and many 
valuable points concerning practical details, see numerous re¬ 
ports, correspondence, and editorials in Engineering News, Jan¬ 
uary to June, 1888 (vol. 19). The above articles contain many 
references to the literature, mostly French, of high masonry dams. 

Art. 3. Rock Fill Dams. 

521 . There are three well-known types of dams, which have 
been in use from time immemorial : earth bank, timber crib-work, 
and masonry. Recent engineering practice on the Pacific coast has 
introduced another type, viz.: the Rock Fill Dam, which is of too 
much importance to pass by without a mention here, although 
strictly it can not be classed as masonry construction. 

A rock fill dam consists of an embankment of irregular stones 
thrown in loosely, except that sometimes the faces are laid by hand. 
If the overflow is to discharge over the crest, the largest stones 
should be placed on the down-stream slope. The dam may be made 
practically water tight (1) by filling the voids with smaller stones, 
gravel, sand, and earth, or (2) by placing any desired thickness of 
earth and puddle on the up-stream face, or (3) by covering the 
water slope with one or more thicknesses of planking, which is calked 
and sometimes also pointed. Either the first or second method 





ART. 2.] 


OUTLINES OF THE DESIGN". 


33& 


would make a dam practically water tight frqm the beginning, and 
it would grow tighter with age ; the third method, if carefully exe¬ 
cuted, would make the dam absolutely water tight at the beginning, 
but would decay, since the upper part of the sheeting would ordi¬ 
narily be alternately wet and dry. 

A great number of rock fill dams have been built on the Pacific 
slope in the past few years, for mining and irrigating purposes. A 
dam of this character has recently been completed on the Hassa- 
yampa River in Arizona, of the following dimensions : “ Height, 
110 ft.; base, 135 ft.; top width, 10 ft.; length on top, 400 ft.; 
water slope, 20 ft. horizontal to 47 ft. vertical (J to 1); back slopes, 
70 ft. horizontal to 180ft. vertical (f to 1); contents, 46,000 cu. yds.; 
cost, by contract, $2.40 per cu. yd.” * It is proposed to build a dam 
of this character in California 250 feet high, which is about 80 feet 
higher than any existing masonry dam, and practically is nearly the 
same amount higher than the proposed Quaker Bridge dam 
(Fig. 72, page 328). 

522. “ Earth dams are good and useful when only still water not 
running over the crest is to be dealt with. Counting reservoir walls 
as dams, which they are, earth dams are vastly more used than any 
other. They must be made with the greatest care, and, if of any 
considerable height, an inner wall of puddle is necessary to their 
integrity. They must be carried down to firm and impervious sub¬ 
soil of some kind, or they are worthless. Any considerable leak is 
at once fatal to them ; and they are also subject to serious injury 
from muskrats, crabs, etc. Nevertheless, many earth dams of 
great age and great height exist, and bid fair to exist for ages, 
showing that it is entirely possible to make them secure.” 

Stone-filled timber cribs have been very much used for dams ; 
but such structures are sure to rot in time, since the timber can not 
always be kept wet. It seems probable that in most instances where 
cribs have been used a rock-fill dam would have been better, 
cheaper, and more durable. 

Masonry dams of all sizes, proportions, and ages exist in great 
abundance, and the entire suitability of masonry for the construction 
of dams is well established. This class of dams is to be preferred 
where large quantities of stone are not near at hand, or where leak¬ 
age is undesirable because of loss of water or of injury to land be- 


* Engineering News, vol. xx. p. 232. 







336 


MASONRY DAMS. 


[CHAP. XIII. 


low, or where space is valuable, or where the surroundings require 
a dam of good appearance. 

523 . “ These three types afford an adequate choice for nearly all 
requirements, but it is obvious that they are open to certain com¬ 
mon objections from which the fourth type—a rock-fill dam—is 
free. They are all comparatively costly ; they require a good deal 
of labor, and much of it skilled and faithful labor, for their con¬ 
struction ; they can only with great inconvenience be constructed 
with water around them, which for the most part must be kept away 
by costly coffer-dams or diversions of channels ; above all, a leak is 
always a source of danger, and is apt to be destructive. They are 
all of them, as it were, during all their existence, in unstable 
equilibrium—all right so long as the balance of forces remains un¬ 
disturbed, and seriously endangered by a variety of causes which 
may disturb it. On the other hand a rock-fill dam is by the very 
process of its construction, if conducted with reasonable judgment, 
a structure which tends to improve with time, and which can not 
be injured but may be benefited by causes which threaten the 
other and more artificial types ; in other words, it is a structure 
which may not be very tight, but which is in stable equilibrium as 
respects all disturbing causes, being improved and never injured by 
them. 

“ A rock-fill dam is appropriate where the bed on which it rests 
is either rock, hard-pan, stiff clay, or some other impervious and 
almost unwashable material. The bed may be more or less over¬ 
laid with gravel or loose material without harm, if it be possible 
to remove the loose material in advance, and if there be current 
enough to remove it from under the foot of the dam, as the work 
of construction progresses, it will not even involve extra expense or 
delay, and the dam may be begun on top of the stratum -without 
apparent regard to it ; but whenever there is any considerable 
stratum of loose material, a rock-fill dam can only be built by back¬ 
ing it with earth or puddle as a timber dam would be, and the 
necessity of providing a proper apron to receive the overflow may 
make a timber or crib dam the more economical. It is obvious 
that the place of all places for the proper use of such a rock-fill 
dam is where leakage is of no importance, either from the loss of 
water or from injury to land below ; where skilled labor is scarce 
and costly, and simplicity of work rather than aggregate quantities 



ART. 2.] 


OUTLINES OF THE DESIGN. 


337 


the important consideration ; where good materials for masonry are 
scarce or absent; and where the surroundings do not demand at¬ 
tention to the question of appearance/’ * 

The greatest economy in this form of dam occurs when the fill 
is made in water ; and it is particularly advantageous in the canali¬ 
zation of rivers, i. e., in forming pools in rivers for the benefit of 
navigation. It has been proposed to use rock-fill dams exclusively 
in the construction of the Nicaragua canal. 

524 . In California the cost of this class of dams varies from $2 
to $3 per cubic yard, including all accessories, which is said to be 
about 50 per cent, cheaper than for earth dams of equal area of 
transverse cross section. 


* Editorial in Engineering News, vol. xx. p. 70. 







CHAPTER XIV. 


RETAINING WALLS. 

625. Definitions. Retaining ivall is a wall of masonry for 
sustaining the pressure of earth deposited behind it after it is built. 
A retaining wall is sometimes called a sustaining wall. 

Face ivall , or slope wall , is a species of retaining wall built 
against the face of earth in its undisturbed and natural position. 
Obviously it is much less important and involves less difficulties 
than a true retaining wall. 

Buttresses are projections in the front of the wall to strengthen 
it. They are not often used, on account of their unsightliness, ex¬ 
cept as a remedy when a wall is seen to be failing. 

Counterforts are projections at the rear of the wall to increase 
its strength. They are of doubtful economjq and were much more 
frequently used formerly than now. 

Land-ties are long iron rods which connect the face of the wall 
with a mass of masonry, a large iron plate, or a large wooden post 
bedded in the earth behind the wall, to give additional resistance to 
overturning. 

Surcharge. If the material to be supported slopes up and back 
from the top of the wall, the earth above the top is called the sur¬ 
charge. 

Retaining walls are frequently employed in railroad work, on 
canals, about harbors, etc.; and the principles involved in their 
construction have more or less direct application in arches, in tun¬ 
neling and mining, in timbering of shafts, and in the excavation of 
deep trenches for sewers, etc., and in military engineering. 

526. Method of Failure. A retaining wall may fail (1) by 
revolving about the front of any horizontal joint, or (2) by sliding 
on the plane of any horizontal joint, or (3) by the bulging of the 
body of the masonry. The first is much the most frequent mode of 

338 


DIFFICULTIES. 


339 


failure, and the second is the least frequent. The wall can not fail 
b}' the center’s bulging out, unless some force acts to keep the top 
from moving forward,—as in a cellar wall, the abutments of arches, 
etc. 

527. Difficulties. In the discussion of the stability of dams, 
it was shown that in order to completely determine the effect of the 
thrust of the water against the wall, it is necessary to know (1) 
the amount of the pressure, (2) its point of application, and (3) 
the direction of its line of action. Similarly, to determine the 
effect of the thrust of a bank of earth against a wall, it is necessary 
to know (1) the amount of the pressure, (2) its point of application, 
and (3) its line of action. The determination of these three quan¬ 
tities requires three equations. The resistance of the wall both to 
sliding and to overturning can be found with sufficient accuracy, as 
has already been explained in Chapter XIII—Dams;—but the 
other elements of the problem are, in the present state of our 
knowledge, indeterminate. 

The origin of the difficulties may be explained briefly as follows. 
A B represents a retaining wall; A D is the sur- z 

face of the ground. The earth has a tendency to 
break away and come down some line as CD. The 
force tending to bring the earth down is its weight; 
the forces tending to keep it from coming down are 
the friction and cohesion along the line CD. The 
pressure against the wall depends upon the form of 
the line CD. If the constants of weight, friction, Fig. 73. 
and cohesion of any particular ground were known, the form of CD 
and also the amount of the thrust on the wall could be determined. 
Notwithstanding the fact that since the earliest ages constructors 
have known by practical experience that a mass of earthwork 
will exert a severe lateral pressure upon a wall or other retaining 
structure, there is probably no other subject connected with the 
constructor’s art in which there exists the same lack of exact ex¬ 
perimental data. This lack is doubtless due, in part at least, to a 
reliance upon theoretical investigations. Of course, mathematical 
investigations unsupported by experiments or experience are a very 
uncertain guide. 

This subject will be discussed further under the heads (1) 
Theoretical Formulas, and (2) Empirical Rules. 














340 


RETAINING WALLS. 


[CHAP. XIV. 


Art. 1. Theoretical Formulas. 

528. A great variety of theories have been presented,, but all rest 
upon an uncertain foundation of assumption, and all are more or 
less defective and self-contradictory. All theories of the stability 
of retaining walls involve the three following assumptions : 

529. First Assumption. All theories assume that the surface 
of rupture, C D, Fig. 73, is a plane. This is equivalent to assum¬ 
ing that the soil is devoid of cohesion, and is inelastic and homo¬ 
geneous, and also that if a mass of such material be sustained by a 
wall, there is a certain plane, called the plane of rupture, along 
which the particles are m equilibrium, i. e., are just on the point of 
moving. This assumption would be nearly correct in the case of 
clean, sharp sand, but would be considerably in error with a tough, 
tenacious soil. 

This assumption gives the data by which the amount of the 
thrust of the earth can be computed; that is to say, this assumjition 
furnishes the conditions from which one of the equations may be 
established. 

530. Second Assumption. A second assumption which is always 
made is that the point of application of the lateral pressure of the 
earth is one third of the height of the wall from the bottom. The 
total pressure on the wall varies as some function of the height; 
and it is assumed to vary as the square of the height, and that 
therefore the center of pressure is at a point two thirds of the 
depth below the top. This is equivalent to assuming that the varia¬ 
tion of the pressure in a mass of earth is the same as in a liquid, 
i. e., that the material is devoid of internal friction. 

This assumption furnishes the second of the equations required 
to determine the effect of the thrust of earth against a retaining 
wall. 

531. Third Assumption. The thircl equation is obtained by 
•assuming the direction of the pressure. There are different theories 
based on different assumptions as to this direction. 

The theories of the stability of retaining walls in most frequent 
use will now be stated, and the underlying assumptions and the 
defects of each will be pointed out. 




ART. 1.] 


THEORETICAL FORMULAS. 


341 



1784 was the first to even approximate the actual conditions, and 
his method is the basis of nearly all formulas used by engineers at 
the present time. It has been taken up and followed out to its 
consequences by Prony (1802), Mayniel (1808), Franqaise (1820), 
Navier (1826), Audoy and Poncelet (1840), Ilagen (1853), Scheffler 
(1857), and Moseley, as well as a host of others, in recent times. 

Coulomb assumed (1) that the line D C, Fig. 73 (page 339), is 
a straight line, down which the prism A CD tends to slide; (2) that 
the resultant pressure is applied at a point two thirds of the depth 
below the top; and (3) that the pressure exerted by this mass on the 
wall'is normal to its back face, which is equivalent to neglecting the 
friction of the earth against the back of the wall. He decomposed the 
weight, W, of the prism A C D, Fig. 74, and the Ann 

reaction, R, of the wall into two components 
respectively, parallel and perpendicular to the 
surface of rupture, D C. The difference of R 



these parallel components, P x — P 9 , he placed 
equal to the prism’s resistance to sliding; and 
-assumed the latter to be equal to ja JFj, in which 


& o 


Fig. 74. 


ju is the co-efficient of friction. There is some prism, A C D, the 


pressure of which against the wall is just sufficient to cause sliding. 


The amount of this pressure will depend upon the weight, w, of a 
unit of volume of the backing; upon the height, h, of the wall; * 
upon the co-efficient of friction, p, of earth on earth; and upon the 
distance A D, which call x. 

Under the conditions assumed, it is possible to state a value of 
R in terms of h, w, g, and x. Coulomb assumed R to vary as x, 
and differentiated the value of R to find the position of the surface 
■of rupture, D C, for a maximum pressure on the wall. This leads 
to the simple conclusion that the lateral pressure exerted by a bank 
of earth with a horizontal top is simply that due to the wedge-shaped 
mass included between the vertical back of the wall and a line bi¬ 
secting the angle between the vertical and the slope of repose of the 
material;* that is, the pressure of the earth against the wall A B, 


* For an algebraic demonstration, see Moseley’s Mechanics of Engineering (2d 
Amer. Ed.), pp. 413-16; for a graphical demonstration, see Van Nostrand’s Engineer¬ 
ing Magazine, vol. ix. p. 202, and vol. xxii. p. 267. 










342 


RETAINING WALLS. 


[CHAP. XIW. 


Fig. 74, is equal to the pressure of the prism ACE sliding along a 
perfectly smooth plane CE, which bisects the angle of repose, A C D. 

No satisfactory proof has been given of the correctness of tln& 
procedure by either Coulomb or any one else; and no defense ha& 
ever been made against a number of serious objections to. 
5 9 it which have been raised. Experiments show that the 

/ lateral pressure of the prism A B C, Fig. 75, between two 
/ boards A B and A C, against A B, “ is quite as much when 
h the board A C is at the slope of repose, 14 to 1, as when it 
FlG - 75, is at half .the angle; and there was hardly any difference 
whether the board was horizontal, or at a slope of to 1, or at 
any intermediate slope.”* , 

533. By this theory the pressure of the wedge A C D (Fig. 
74) is 

P — \ w h* tan 2 \A CD ..(1) 

in which w is the weight of a unit of the material to be supported, 
and li is the height of the wall. This thrust is assumed to act two 
thirds of A C, Fig. 74, below A. Or, in other words, the thrust of 
the prism is equivalent to the pressure of a liquid whose weight per 
unit of volume is w tan 2 ^ A CD. 

Equating the moment of the overturning force and the moments- 
of resistance in terms of the unknown thickness, and solving the 
equation, gives the thickness which the wall must have to be on the 
point of overturning. For example, assume that it is desired to 
determine the thickness, t, of a vertical rectangular wall. Repre¬ 
sent the weight of a cubic foot of the masonry by W. Then placing 
the moment of the wall equal to the amount of the thrust of the 
earth, gives 

W h t . t — P . li .. . (2) 

Solving equations (1) and (2) gives 

/ 

t — h tan CD \/ .(3) 


* Benj. Baker, an eminent English engineer, in a very interesting and instructive 
article on “ The Actual Lateral Pressure of Earthwork,” reprinted in Van Nostrand’s 
Engineering Magazine, vol. xxv. pp. 333-42, 353-71, and 492-505, from Proc. of the 












ART. 1.] 


THEORETICAL FORMULAS. 


343 


Numerous tables have been computed which give, to a great 
number of decimal places, the thickness of a rectangular wall in 
terms of its height, the arguments being the ratio of the weights of 
a unit of volume of the wall and backing, and the angle of repose. 
Such tables are of but little practical value, as will appear presently. 

534. Surcharged Walls. The rule that the plane of rupture 
bisects the angle between the natural slope of the earth and the back 
of the wall, holds good only when the top surface of the bank is 
horizontal and the back of the wall vertical. The formula for a 
surcharged wall, or for the case in which the back is not vertical, 
or for both combined, may be deduced* * * § in the same general way as 
above; but the results for each case are too complicated for ordinary 
use. and each is subject to the same errors as the formula for a ver¬ 
tical wall and level top surface. There are a number of exceedingly 
ingenious graphical solutions of the resulting equations, f 

535. Reliability of Coulomb’s Theory. It is generally conceded 
that the results obtained by this method have but little practical 
value. “ Experiments and practical experience show that walls, 
which according to this theory are on the point of overturning, 
possess on the average a factor of safety of about two” J One of 
the author’s students experimented with fine shot, which appear to 
fulfill the fundamental assumptions of this theory, and found that 
the observed resistance was 1.97 times that computed by CoulomVs 
formula.§ The uncertainties of the fundamental assumptions and 
the questionableness of some of the mathematical processes are 
sufficient explanation of the difference between the theory and 
practice. 

536. WEYRATJCH’S Theory. This is the latest one, having been 
proposed in 1878. It was first brought to the attention of American 
engineers by Professor J. A. Du Bois's translations of WinkleEs 
« Neue Theorie des Erddruckes,” and Weyrauch’s paper on retain¬ 
ing walls published in “ Zeitscbrift fur Baukunde,” 1878, Band i. 
Heft 2, which translation was published in the Journal of the Frank- 

* See Moseley’s Mechanics of Engineering, pp. 424-26. 

t See Van Nostrand’s Engineering Magazine, vol. ix. p. 204 ; and do., vol. xxv. 
p. 355. For references to elaborate graphical treatises on retaining walls, see Du 
Bois’s Graphical Statics, pp. lv-lvi of Introduction. 

+ Benj. Baker in “ The Actual Lateral Pressure of Earthwork.” See foot-note on 

page 342. 

§ See M. Fargusson’s Bachelor’s Thesis, University of Illinois. 








344 


RETAINING WALLS. 


[CHAP. XIV,. 


lin Institute, vol. cviii. pp. 361-87. The following presentation of 
this theory is drawn mainly from that article. 

This theory assumes (1) that the surface of rupture is a plane* 
(2) that the point of application of the resultant of the lateral 
pressure of the earth is at a point one third of the height of the 
wall from the bottom, and (3) that there is no friction between the 
earth and the back of the wall. It is claimed that these three are 
the only assumptions involved in this theory, and that the direction 
of the resultant pressure is deduced from the fundamental rela¬ 
tions necessary for equilibrium under the conditions assumed. 

The analysis to establish the equations for the amount and direc¬ 
tion of the thrust of the earth is too long and too complicated to be 
attempted here; consequently, only the final equations will be 
given. 



e = the augle of the upper surface with the horizontal. 
f3 = the angle of the plane of rupture with the vertical. 

0 = the angle of repose with the horizontal. 

537. General Formulas. For a plane earth-surface, horizontal 
or sloping up at any angle, and the back of the wall vertical or 
leaning forward at any angle, the general relations are * 


in which 


E = 


cos (0 — a) ~T 7i 2 w 
(n 1) cos aj 2 cos (a -j- d)* 



n _ i/ sin (<P+ tf) sin (<p - e) 

' cos (o' -j- d) cos (a — e)* 



* See Howe’s Retaining Walls for Earth, pp. 46, 47; and also Van Nostrand’s. 
Engineering Magazine, vol. xxii. pp. 265-77. 




































THEORETICAL FORMULAS. 


345 


T. 1.] 


The value of d required in (5) can be deduced from 


tan d = 


sin (2 a — e) — K sin 2 (a — e) 


K — cos (2 a — e) -|- K cos 2 (a — e)’ 


• • 


in which 


K = 


cos e — V cos 2 e — cos 2 0 
cos 2 0 


(O 

(?) 


538. Horizontal Earth-surface. If the upper surface of the 
earth is horizontal, then e = 0, and 


tan a If iv 
~ sin {a 6) 2 



and d can be found from 


tan 6 = 


sin <fi sin 2 a 
1 — sin 0 cos 2 a 



If the back of the wall is vertical, a — 0; and equation (9) 
gives d = 0. Therefore 

^=tan s (45°-|)~*. (10) 

539. Surcharge at the Natural Slope. If the upper surface of 
earth has the natural slope, e = (p; and therefore 


E- 


'cos (0 — « , ) _ | 2 w 

cos nr J 2 cos (a + d)’ 


( 11 ) 


and d is determined from 


tan d = 


sin 0 cos ( 0 — 2 a) 

1 — sin 0 sin (0 — 2 a)' 


( 12 ) 


If the back of the wall is vertical, a = 0, and d = 0, which 
shows that E acts parallel to the top surface of the earth. In this 
case 

E = i cos 0 If iv .(13) 


* Compare with equation (1), page 342. 


























34 G 


RETAINING AVALLS. 


[CHAP. XIV. 


540. The general equations for WFyrauch’s theory, viz., equa¬ 
tions (4), (5), (G), and (7), have not been solved for any special 
case, except for e = 0, and e = <fi. The reduction is very long and 
tedious. 

541. The formulas for each of the above cases may be solved 
graphically,* * * § but the explanations are too long to be given here. 

542. Reliability of Weyrauch’s Theory. On behalf of this 
theory it is claimed f that the only errors in it are those due to the 
neglect of the cohesion of the backing, and to assuming that the 
surface of rupture is a plane ; and also that “ it is free from all the 
objections which may be urged against all others, and can be used 
with confidence.” These claims are not supported by the facts. 

WeyrauclTs theory is unquestionably subject to any errors which 
may be involved in the assumptions that the surface of rupture is a 
plane (see § 529), and that the point of application of the resultant 
pressure of the earth is at two thirds of the height of the Avail from 
the top (see § 530). Second, the analysis purports to be perfectly 
general; J but it is evidently inapplicable to a Avail inclined toward 
the earth to be supported, since the formulas make the thrust of 
the earth increase with the backward inclination of the Avail. In 
fact the theory makes no difference betAveen a Avail leaning forward 
and one leaning backward. For a Avail inclining at the angle of 
repose, it gives a very great lateral pressure—see eqs. (8) and (9). 
Third, the mathematical process of determining the position of the 
surface of rupture is at least questionable. Fourth, the theory errs 
on the safe side, because it neglects a vertical component of the 
earth pressure which is independent of friction. § 

Weyrauch’s theory differs from Coulomb’s only in the form of 
the results and in the manner of deducing them ; || and hence is of 
no practical value. 

543. Weyrauch’s method of deducing the direction of the earth 


* See Jour. Frank. Inst., vol. cviii. pp. 3S0-85; Van Nostrand’s Engineering 
Magazine, vol. xxii. pp. 266-73 ; Howe’s Retaining A\ r alls for Earth, pp. 7-12. 

t By its author, Prof. AVeyrauch, and also by the translator, Prof. Du Bois,—see 
Jour. Frank. Inst., vol. cviii. pp. 486-87. 

X See Jour. Frank. Inst., vol. cviii. p. 377; and also Howe’s Retaining AValls for 
Earth, p. 2. 

§ In proof that such a component exists, see experiments by Siegler in Annales de» 
Ponts et Chausses , reprinted in Scientific American Supplement , vol. xxiv. pp. 9724-25. 

| Van Nostrand’s Engineering Magazine, vol. xxii. pp. 265-77. 





THEORETICAL FORMULAS. 


347 


1RT. 1.] 

pressure assumes that there is no friction between the earth and the 
back of the wall, or, in other words, that the angle, 6, which the 
thrust of the earth makes with the back of the wall, does not de¬ 
pend upon the structure of the wall for its value. The formula in 
this form fails to agree with ordinary experience ; and hence it 
has been proposed * to modify the general formula by considering 
that the angle between the resultant pressure of the earth and the 
back of the wall is never less than the angle of friction between the 
earth and the wall. The method of doing this is as follows: 

If 0' represents the co-efficient of friction between the earth 
and the wall, then the direction of E must make an angle with the 
normal to the back face of the wall equal at least to 0'. To intro¬ 
duce 0' into Professor Weyrauclds theory, it is necessary to find the 
value of 6 as given by his formula, and see if it is greater or less than 
0'. If it is less, use the value of 0' to determine the direction of 
E ; if greater, use the value of d and omit 0' altogether. The 
value of 0' can not be determined accurately; but unless the back 
of the wall is exceedingly smooth, 0' will be greater than 0. If 
the back of the wall is rough rubble (§ 213) or is stepped, 0'will be 
considerably larger than 0. If the friction between the earth and 
the wall be neglected, i. e., if it is assumed that 0' = 0, then when 
rough rubble retaining walls are proportioned according to Wey- 
rauch’s theory, they will have a factor of safety considerably larger 
than appears from the computations. 

This modification is inconsistent with the general the Dry, since 
tlie fundamental equations were established for that value of d which 
Mould produce equilibrium, and the corresponding value of the 
tlrust was deduced accordingly. It is certainly incorrect to use one 
direction in determining the value of the thrust and another in 
applying it. Further, it is not reasonable to believe that the thrust 
ever makes an angle with the normal to the back of the wall 
greater than the angle of friction, since one of the fundamental 
conditions of statics is that if the resultant pressure makes an angle 
witl the normal greater than the angle of repose, motion takes 
placi. This modification of Weyrauclds theory purports to give the 
relations for a state of equilibrium, and yet violates the fundamental 
oondtion necessary for equilibrium. Neither the original theory 
nor tie above modification of it are of any practical value. 


* ly Prof. Cain in Van Nostrand’s Engineering Magazine, vol. xxv. p. 92. 








348 


DETAINING WALLS. 


[CHAP. XIV. 


544. Rankine’s Theory. There is another class of theories, 
which, in addition to the assumptions of § 530 and § 531, assume 
that the thrust of the earth makes an angle with the back of the 
wall equal to the angle of repose of the earth. Different writers 
arrive at their results in different ways, but most of them proceed 
irom a consideration of the conditions of equilibrium of the earth 
particles, and arrive at their results by integration. Of the formulas 
deduced in the latter way, Rankine’s * are the best known. All the 
theories of this class have essentially the same limitations and de¬ 
fects as Coulomb’s and Weyrauch’s. 

545. Applicability of Theoretical Formulas. It is generally 
conceded that the ordinary theories—Coulomb’s, Weyrauch’s, and 
Rankine’s,—types of the only ones for which there is any consider¬ 
able show of reasonableness,—are safe ; but “ to assume upon theo¬ 
retical grounds a lateral thrust which practice shows to be excessive, 
and then compensate for it by giving no factor of safety to the wall, 
although the common way, is not a scientific mode of procedure.’’ 
This is only another reason for the statement, already made, that 
theoretical investigations are of but little value in designing re¬ 
taining walls. The problem of the retaining wall is not one that 
admits of an exact mathematical solution; the conditions can not be 
expressed in algebraic formulas. Something must be assumed ir 
any event, and it is far more simple and direct to assume the thick¬ 
ness of the wall at once than to derive the latter from equations 
based upon a number of uncertain assumptions. 

Bear in mind that none of the above formulas apply if the back 
of the wall inclines towards the earth to be supported, or if t\e 
wall has a curved profile, or if the upper surface is irregular. It 
seems to be conceded that in these cases the surface of rupture is 
not a plane, and hence no theory yet proposed will apply. 

In this connection it seems necessary to warn the student lhat 
not all theories for retaining walls are as nearly correct as tlose 
referred to above. Some of them, although having all the predige 
of antiquity and offering the advantages of extended tables for 'heir 
application, are totally valueless, being based upon unwarnnted 
assumptions, and violating the fundamental principles of mechanics. 

546. Theoretical investigations of many engineering problems 
which in every-day practice need not be solved with extreme accu- 


* Civil Engineering, pp. 401-07. 











ART. 2.] 


EMPIRICAL RULES. 


34& 


racy, are useful in determining the relations of the various elements 
involved, and thus serve as a skeleton about which to group the 
results of experience ; but the preceding discussion shows that the 
present theories of the stability of retaining walls are not sufficiently 
exact to serve even as a guide for future investigations. Further¬ 
more, the stability of a retaining wall is not a purely mathematical 
problem. Often the wall is designed and built before the nature of 
the backing is known; and the variation of the backing, due to rain, 
frost, shock, extraneous loads, etc., can not be included in any 
formula. 

Art. 2. Empirical Rules. 

547. ENGLISH Rules. The eminent English engineer Benjamin 
Baker, who has had large experience in this line in the construc¬ 
tion of the underground railroads of London, says, “Experience 
has shown that a wall [to sustain earth having a level top surface], 
whose thickness is one fourth of its height, and which batters 1 or 
2 inches per foot on the face, possesses sufficient stability when the 
backing and foundation are both favorable. This allows a factor of 
safety of about two to cover contingencies. It has also been proved 
by experience that under no ordinary conditions of surcharge or 
heavy backing is it necessary to make a retaining wall on a solid 
foundation more than double the above, or one half of the height in 
thickness. Within these limits the engineer must vary the strength 
according to the conditions affecting the particular case. Outside 
of these limits, the structure ceases to be a retaining wall in the 
ordinary acceptation of the term. As a result of his own experi¬ 
ence, the author [Benj. Baker] makes the thickness of retaining 
walls in ground of an average character equal to one third of the 
height from the top of the footings. 

Hundreds of revetments have been built by royal engineer 
officers in accordance with Glen. Fanshawe’s rule of some fifty years 
ago, which was to make the thickness of a rectangular brick wall, 
retaining ordinary material, 24 per cent, of the height for a batter 
of -J-, 25 per cent, for 26 per cent, for £, 27 per cent, for T V, 28 per 
cent, for T \, 30 per cent, for Jj-, and 32 per cent, for a vertical wall/ ” * 

548. TRAUTWINE’S Rule. Trautwinef recommends that “ the 

* Van Nostrand’s Engineering Magazine, vol. xxv. p. 370, from Proc. Inst, of 
C. E. 

+ Engineer’s Pocket-Book (Ed. 1885), p. 683. 







350 


RETAINING WALLS. 


[CHAP. XIV. 


thickness of the top of the footing course of a vertical or nearly 
vertical wall which is to sustain a backing of sand, gravel, or earth, 
level top surface, when the backing is deposited loosely (as when 
dumped from cars, carts, etc.), for railroad practice, should not be 
less than the following : 

Wall of cut-stone, or of first-class large-ranged rubble in mortar, 35 per cent. 


“ “ good common scabbled mortar-rubble, or brick. 40 per cent. 

“ " well scabbled dry rubble. 50 per cent. 


When the backing is somewhat consolidated in horizontal layers, 
each of these thicknesses may be reduced; but no rule can be given 
for this. Since sand or gravel has no cohesion, the full dimensions 
as above should be used, even though the backing be deposited in 
layers. A mixture of sand, or earth with pebbles, paving stones, 
bowlders, etc., will exert a greater pressure against the wall than 
the materials ordinarily used for backing; and hence when such 
backing has to be used, the above thicknesses should be increased, 
say, about i to ^ part.” 

549. Details of Construction. The arrangement of the foun¬ 
dation of a retaining wall is an important matter, but has already 
been sufficiently discussed (see Part III, and also §§ 491 and 551). 
It is universally admitted that a large majority—by some put at 
nine out of ten, and by others at ninety-nine out of a hundred—of 
failures of retaining walls are due to defects in the foundation. 

Retaining walls are constructed of ashlar or brick, or of either 
ashlar or brick backed with rubble, or of rubble either with mortar 
or dry. As the pressure at each bed-joint is concentrated towards 
the face of the wall, the larger and most regular stones should be 
placed on the front. Occasional stones or even courses should 
project beyond the back of the wall, so that the backing can rest 
upon them, thus increasing the resistance of the wall to overturn¬ 
ing. This object is also promoted by building the back in steps. 
The coping should consist of large flat stones extending clear across 
the wall. 

As a rule, the greatest thrust comes against retaining avails when 
the mortar is green and least able to resist it, which is a reason for 
preferring cement to lime mortar. If the backing is to be filled in 
before the mortar hardens, it should be deposited in thin, horizon¬ 
tal layers, or the wall should be supported temporarily by shores. 

550. Drainage. Next to a faulty foundation, water behind the 







ART. 2.] 


EMPIRICAL RULES. 


351 


wall is the most frequent cause of the failure of retaining walls. 
The water not only adds to the weight'of the backing material, but 
also softens the material and changes the angle of repose so as to 
greatly increase its lateral thrust. With clayey soil, or any material 
resting upon a stratum of clay, this action becomes of the greatest 
importance.' To guard against the possibility of the backing’s be¬ 
coming saturated with water, holes, called weepers, are left through 
the wall. One weep-hole, three or four inches wide and the depth 
of a course of masonry, is generally sufficient for every three or 
four square yards of front of the wall. When the backing is clean 
sand, the weep-holes will allow all the water to escape ; but if the 
backing is retentive of water, a vertical layer of stones or coarse 
gravel should be placed next to the wall to act as a drain. An 
ordinary drain at the back of the wall is often useful. 

When the backing is liable to be reduced to quicksand or mud 
by saturation with water, and when this liability can not be removed 
by efficient drainage, one way of making provision to resist the 
additional pressure which may arise from such saturation is to cal¬ 
culate the requisite thickness of wall as if the earth were a fluid. 
A puddle-wall is sometimes built against the back of dock-walls to 
keep out the water. 

The resistance of the wall to sliding is materially increased by 
laying the lower courses of masonry with an inclination inward. 
An objection to inclining the joints, particularly in dry masonry, 
is that the water will enter them and be carried to the backing. 
This objection is sometimes met by building the face with horizon¬ 
tal courses, and inclining the courses in the back of the wall. The 
back of the wall for 2 or 3 feet from the top should have a batter 
of at least 1 inch in 1 foot, in order that the frost may lift the 
earth and not break the joints of the masonry. 

Walls are sometimes built with both faces inclined toward the 
material to be supported, and sometimes with a curved profile ; but 
it is generally considered unwise to do either, owing to the extra 
expense and trouble in construction. 

551. Land Ties. Retaining walls may have their stability in¬ 
creased by being tied or anchored by iron rods to vertical plates of 
iron or blocks of stones imbedded in a firm stratum of earth at a 
distance behind the wall. “ The holding power, per foot of breadth, 
of a rectangular vertical anchoring plate, the depth of whose upper 



352 


RETAINING WALLS. 


[CHAP. XIY. 


mid lower edges below the surface are respectively x x and x 2 , may 
be approximately calculated from the following formula : 


H=w 


x„ 


— x x 4 sin 0 


2 cos 2 0 , 


(14) 


in which H is the holding-power of the plate in pounds per foot of 
breadth, w is the weight in pounds of a cubic foot of the earth, 
and 0 its angle of repose. The center of pressure of the plate is 
about two thirds of its height below its upper edge,—at which point 
the tie-rod should be attached. 

“If the retaining wall depends on the tie-rods alone for its 
security against sliding forward, they should be fastened to plates 
on the face of the wall in the line of the resultant pressure of the 
earth behind the wall, that is, at one third [see § 530] of the height 
of the wall above its base. But if the resistance to sliding forward 
is to be distributed between the foundation and the tie-rods, the 
latter should be placed at a higher level. For example, if half the 
horizontal thrust is to be borne by the foundation and half by the 
tie-rods, the latter should be fixed to the wall at two thirds of its 
height above the base.” * 

552. Relieving Arches. In extreme cases, the pressure of the 
earth may be sustained by relieving-arches. These consist of a row 

of arches having their axes and the faces of their 
piers at right angles to the face of a bank of earth. 
There may be either a single row of them or several 
tiers; and their front ends may be closed by a ver¬ 
tical wall,—which then presents the appearance of 
a retaining wall, although the length of the arch¬ 
ways is such as to prevent the earth from abutting 
against it. Fig. 77 represents a vertical transverse 
section of such a wall, with two tiers of relieving arches be¬ 
hind it. 

To determine the conditions of stability of such a structure as a 
whole, the horizontal pressure against the vertical plane OD maybe 
determined, and compounded with the weight of the combined 
mass of masonry and earth OAED, to find the resultant pressure 
on the foundation. 



Fig. 77. 


* Rankine’s Civil Engineering, p. 411. 














CHAPTER XV. 


BRIDGE ABUTMENTS. 

• 

653. General Forms. There are four forms of abutments in 
more or less general use. 1. A plain wall parallel to the current, 
shown in elevation at Fig. 78, with or without the wings A D A and 
BEG. The slopes may be finished with an inclined coping, as 
A D, or offset at each course, as B E —usually the latter. This form 
may appropriately be called the straight abutment. 2. The wings 
may be swung around into the bank at any angle, as shown (in plan) 
in Fig. 79. The angle 0 is usually about 30°. This form is known 



as the icing abutment. 3. When 0 of Fig. 79 becomes 90°, we have 
Fig. 80, which is called the U abutment. 4. If the wings of Fig. 
80 are moved to the center of the head-wall, we get Fig. 81, which 
is known as the T abutment. 

The abutment of an ordinary bridge has two offices to perform, 
viz., (1) to support one end of the bridge, and (2) to keep the earth 
embankment from sliding into the water. In Fig. 78, the portion 
D E G F serves both these purposes, while the wings A D F and 
BEG act only as retaining walls. In Figs. 79 and 80, the portion 
D E performs both offices, while the wings A D and B E are merely 
retaining walls. In Fig. 81 the “head” D E supports the bridge, 
and the “ tail,” or “stem,” A B carries the train; hence the whole 
structure acts as a retaining wall and also supports the load. The 
abutment proper may fail (1) by sliding forward, (2) by bulging, or 
(3) by crushing; however, it is improbable that it will fail by sliding 
forward. Its dimensions are to be determined as for a retaining 
wall (Chap. XIV); but the mathematical theory of the lateral 

353 


















354 


BRIDGE ABUTMENTS. 


[CHAP. XV. 


pressure of earth is a much less perfect guide for designing bridge 
abutments than it is for simple retaining walls. The weight of the 
bridge helps the abutment to resist the thrust of the earth; bub on 
the other hand, the weight of the train on the embankment in¬ 
creases the lateral pressure against the abutment. 

554. The form of the abutment to be adopted for any particular 
case will depend upon the locality,—whether the banks are low and 
flat, or steep and rocky; whether tlm current is swift or slow; and 
also upon the relative cost of earthwork and masonry. If the shore 
is flat, and not liable to be cut away by the current, an abutment 
like Fig. 78 will be sufficient and most economical. However, this 
form is seldom used, owing to the danger of the water’s flowing 
along immediately behind the wall. 

The form of Fig. 79 may be adopted when there is a contraction 
of the waterway at the bridge site, sinoe deflecting the wing walls, 
above and below, slightly increases the amount of water that can 
pass. This advantage can be obtained, to some degree, with the 
straight abutment (Fig. 78) by thinning the wings on the front and 
leaving the back of the wings and abutments in one straight line. 
There is not only no hydraulic advantage, but there is a positive 
disadvantage, in increasing the deflection of the wings beyond, say, 
10° or 15°. The more the wing departs from the face line as it 
swings round into the embankment, the greater its length and also 
the greater is the thrust upon it. The wings are not usually ex¬ 
tended to the toe, B, of the embankment slope, but stop at a height, 
depending upon the angle of deflection and the slope, such that the 
earth flowing around the end of the wall will not get into the chan¬ 
nel of the stream. It can be shown mathematically that, if the toe 
of the earth which flows around the end of the wing is to be kept 
three or four feet back from the straight line through the face of 
the abutment, an angle of 25° to 35° is best for economy of the 
material in the wing walls. This angle varies slightly with the pro¬ 
portions adopted for the wing wall and with the details of the 
masonry. This form of construction is objectionable, since the 
foot of the slope in front of the wing is liable to be washed away ; 
but this could be remedied somewhat by riprapping the slope, or, 
better, by making the wings longer. 

Fig. 78 is one extreme of Fig. 79, and Fig. 80 is the other. As 
the wing swings back into the embankment the thrust upon it in- 



WING ABUTMENT. 


355 


creases, reaching its maximum at an angle of about 45°; when the 
wing is thrown farther back the outward thrust decreases, owing to 
the filling up of the slope in front of the wing. Bringing the wings 
perpendicular to the face of the abutment, as in Fig. 80, also de¬ 
creases the lateral pressure of the earth, owing to the intersection of 
the surfaces of rupture for the two sides, which is equivalent to re¬ 
moving part of the “prism of maximum thrust.” If the banks of 
the stream are steep, the base of the wing walls of Fig. 80 may be 
stepped to fit the ground, thereby saving masonry. Under these 
conditions, also the wing abutment, Fig. 79, can be treated in the 
same way; but the saving is considerably less. When the masonry 
is stepped off in this way, the angle thus formed becomes the weak¬ 
est part of the masonry; but, as the masonry has a large excess of 
strength, there is not much probability of danger from this cause, 
provided the work is executed with reasonable care. 

555. Fig. 81 is the most common form of abutment. For equal 
amounts of masonry, wing abutments give better protection to the 
embankments than T abutments. The latter are more stable, be¬ 
cause the center of gravity of the masonry is farther back from the 
line of the face of the abutment, about which line the abutment 
must turn or along which it will first crush. The amount of ma¬ 
sonry in tall T abutments can be decreased by building the tail wall 
hollow, or by introducing arches under it. The more massive the 
masonry, the cheaper it can be constructed; and, for this reason, it 
is probable that the simple T abutment is cheaper than the U abut¬ 
ment, although the latter may have less masonry in it. On the other 
hand, the opportunities for inspecting the masonry during construc¬ 
tion are better with the U than with the T abutment, and hence the 
former is usually better built than the latter. This is an important 
item, since it is somewhat common for railroad masonry to fail by 
being shaken to pieces by the passage of trains. 

556. Wing Abutment. Fig. 82 shows a common form of the 
wing abutment. This one is finished with stone pedestal blocks— 
marked B in plan, A in elevation, and C in section,—which is not 
always done. The thickness of pedestal blocks and the thickness 
of the coping under the pedestal blocks vary slightly with the span 

•(see § 558). The height of the parapet wall, or dirt wall (the wall 
which keeps back the top of the embankment, marked P W in 
section), will vary with the style of the bridge, but should not have- 




356 


BRIDGE ABUTMENTS. 


[CHAP. XY. 


a thickness less than four tenths of its height (see §§ 547 and 548). 
The bridge often rests directly upon the coping. The top dimen¬ 
sions of the abutment will depend somewhat upon the size and 
form of bridge : but for railroad bridges it will usually not be less 
than 5 ft. wide by 20 ft. long, nor more than 6 ft. by 22 ft. 



u, 

Z 

lx) 

ci § 
o h 

D 


0 

H 

fa 


CQ 

< 

o 

z 


Ul 

ul 


ui 

< 

O 

05 



The usual batter is 1 in 12; sometimes 1 in 24. For heights' 
under about 20 ft., the top dimensions and the batter determine the 
thickness at the bottom. For greater heights, the quite uniform 













































































WING ABUTMENT, 


357 


\ 


TABLE 37. 

Quantity of Masonry in Wing Abutments of the General Form 

shown in Fig. 82. See § 557. 


Height op Abutment- 
Foundation to Coping. 

Dimensions op the 
Bottom op Abutment. 

Area op Lowest 
Course. 

Masonry in one Abutment, 
exclusive of Footing, 
Copings, and Pedestals.* 

Width of the 
Head. 

Thickness of the 
Head. 

Length of Face 
of Wing. 

One Head. 

Two Wings. 

Total. 

j 

One Head Wall. 

Two Wing Walls. 

Parapet. 

Total. 

feet. 

feet. 

feet. 

feet. 

sq ft. 

sq.ft. 

sq. ft. 

| 

cu. ft. 

cu. ft. 

cu. ft. 

cu . yds. 

5 

22.2 

6.8 

18.9 

151 

165 

316 

709 

640 

230 

57.7 

6 

22.2 

7.0 

20.6 

155 

184 

339 

863 

821 

230 

70 8 

7 

22.3 

7.2 

22.3 

161 

203 

364 

1.021 

1,020 

230 

84.1 

8 

22.3 

7.3 

24.0 

163 

223 

386 

1,183 

1,238 

230 

98.1 

9 

22.4 

7.5 

25.7 

168 

243 

411 

1.348 

1,475 

230 

113.0 

10 

22.4 

7.7 

27.4 

172 

264 

436 

1.518 

1,732 

230 

128.8 

11 

22.5 

7.8 

29.1 

176 

285 

461 

1.692 

2,011 

230 

145.6 

12 

22.5 

8.0 

30.8 

180 

306 

486 

1.869 

2,310 

230 

162.6 

• 13 

22.5 

8.2 

32.5 

185 

328 

513 

2 052 

2,632 

230 

182.0 

14 

22.6 

8.3 

34.2 

188 

351 

539 

2,238 

2.975 

230 

201.6 

15 

22.6 

8.5 

35.9 

192 

374 

566 

2.429 

3.341 

230 

222.2 

16 

22.7 

8.7 

37.6 

197 

398 

595 

2.623 

3.731 

230 

243.8 

17 

22.7 

8.8 

39.4 

200 

422 

622 

2,822 

4.144 

230 

266.5 

18 

22.7 

9.0 

41.0 

204 

447 

651 

3.024 

4,580 

230 

290.1 

19 

22.8 

9.1 

42.8 

207 

472 

679 

3,232 

5,041 

230 

314.9 

20 

22.8 

9.3 

44.5 

212 

497 

709 

3,442 

5,526 

230 

340.6 

21 

22.9 

9 5 

46.2 

217 

523 

740 

3.657 

6,038 

230 

367.5 

22 

22.9 

9.7 

47.9 

222 

550 

772 

3.876 

6.577 

230 

395.6 

23 

23.0 

9.8 

49.6 

225 

577 

802 

4,100 

7,143 

230 

424.9 

24 

23.0 

10.0 

51.3 

230 

604 

834 

4,327 

7,735 

230 

455.3 

25 

23.0 

10.2 

53.0 

235 

633 

868 

4.559 

8,354 

230 

486.7 

26 

23.1 

10.3 

54.7 

238 

661 

899 

4,796 

9,002 

230 

519.5 

27 

23.1 

10.5 

56.4 

243 

690 

933 

5,036 

9.678 

230 

553.4 

28 

23 2 

10.7 

58.1 

248 

720 

968 

5.281 

10.384 

230 

588.7 

29 

23.2 

10.8 

59.8 

251 

750 

1,001 

5,530 

11.120 

230 

625.1 

30 

23 3 

11.0 

61.5 

256 

780 

1,036 

5,784 

11,886 

230 

662.9 

31 

23.3 

11.2 

63.2 

261 

811 

1,072 

6.041 

12,682 

230 

701.9 

32 

23.3 

11.3 

64.9 

263 

843 

1,106 

6,303 

13,509 

230 

742.9 

33 

23 4 

11.5 

66.6 

269 

815 

1,144 

6,569 

14,369 

230 

784.0 

34 

23.4 

11.7 

68.4 

273 

907 

1,180 

6,841 

15,259 

230 

827.0 

35 

23.5 

11.8 

70.1 

277 

940 

1,217 

7,116 

16.182 

230 

871.4 

36 

23.5 

12.0 

71.8 

282 

973 

1,255 

7,395 

17,139 

230 

917.2 

37 

23 6 

12 2 

73.5 

288 

1,007 

1,295 

7,679 

18,127 

230 

964.2 

38 

23.6 

12.3 

75.2 

290 

1,042 

1,332 

7,967 

19,150 

230 

1,012.8 


* Dimension stone in two pedestal blocks. 

“ “ “ coping of one abutment 


= 64 cu. feet. 
= 234 “ “ 


Total dimension stone in “ 


= 298 “ “ 


rule is to make the thickness four tenths of the height. The amount 
of masonry in the abutment is computed in accordance with this 
rule, although the actual quantity is usually more than that required 
by it. Since there is no objection to the walks being rough, no 
























































358 


BRIDGE ABUTMENTS. 


[CHAP. XT. 


stones are cut out to secure the specified thickness, and hence the 
actual quantity of masonry usually exceeds the amount required. 
The spread of the footing courses and foundation will depend, of 
course, upon the location. 

The wings should be proportioned according to the rules for 
retaining walls (see §§ 547 and 548). The wings are not always pro¬ 
longed u*ntil their outer ends intersect the foot of the embankment 
slope; but are frequently stopped with an end height of 3 to 5 feet 
above the footing. The thickness of the wing wall decreases from 
the body of the abutment toward the tail in proportion to the height. 
For appearance, the top of the wing is usually made uniform from 
head to tail, being usually from 2| to 3| feet, according to the size 
of the structure. The steps should be capped with stones, not less 
than 1 foot thick, covering the entire step and extending under the 
step above not less than 1 foot. 

557. Contents of Wing Abutments. The table on page 357 
gives the quantities of masonry in wing abutments of the form 
shown in Fig. 82. Since the outlines of such structures are not 
simple geometrical figures, it is necessary to make more or less ap¬ 
proximations in computing the cubical contents. For example, in 
Fig. 82 the wings are stepped off to fit the slope of the emba nkment 
as shown; and hence the corner of each course projects bejond the' 
earthwork. The amount of masonry in these projecting corners 
varies as the thickness of the courses, and for any particular abut¬ 
ment it could be found accurately; but, in computing a table of 
general results, it is necessary to assume some thickness for the 
courses. In this case the courses were assumed to be 1 foot thick. 
Idle back of the “ head ” was assumed to conform strictly to the batter 
line, although in construction it would be stepped. The dimensions 
of the parapet wall will vary with the thickness of the pedestal 
blocks used, and also with the style of the bridge. The contents 
of the parapet as given in the table are for the dimensions shown in 
Fig. 82. 

Footing courses were not included in the table, since they vary 
with the nature of the foundation. The area of the lowest course 
of masonry is given, from which the areas of the footing courses and 
of the foundation pit may be determined. The thickness at the 
top and the batter, as in Fig. 82, give, for any height found in the 
table, a thickness of wall at the bottom of at least four tenths of its 



U ABUTMENT. 


359 


height (see §548); for heights greater than in the table, the back 
of the wall must be stepped to keep the thickness four tenths of the 
height.* 

558. U ABUTMENT. Fig. 83 shows the standard plans of the 
Atchison, Topeka and Santa Fe R. R.f for U abutments. This is 
the only form of bridge abutment used on this road, except in 
special cases. The T abutment was once the standard, but was 
abandoned about fifteen years ago.| 

Tfie specifications under which these abutments are built, require 
as follows : “ 1. Bed-plate pedestal blocks to be 2 feet thick, and 
placed symmetrically with regard to the plates. 2. Coping under 
pedestal blocks to be 18 inches thick for all spans exceeding 100 
feet, 16 inches for 90 feet, and 14 inches for spans under 90 
feet,—said coping to be through stones, and spaced alike from both 
sides of abutment. 3. Distances from front of dirt wall to front 
of bridge seat, and from grade line to top of bridge seat, and 
thickness of dirt wall, to vary for different styles and lengths of 
bridges. 4. Front walls to be 22 feet wide under bridge seat for 
all spans of 100 to 160 feet inclusive. 5. Total width of bridge 
seat to be 5 ? feet, for all spans. 6. Steps on back of walls to 
be used only when necessary to keep thickness of the height. 
7. In case piling is not used, footing courses may be added to give 
secure foundation. 8. Length of wing walls to be determined by a 
slope of 1^ to 1 at the back end of the walls—as shown by dotted 
line in front elevation,—thence by a slope of 1 to 1 down the outside 
—as shown on side elevation—to the intersection of the ground line 
with face of abutment. This rule may be modified in special cases. 
9. Dimensions not given on the drawing are determined by the 
style and length of bridge, and are to be found on special sheet.” 

559. Although this road is noted for the excellency of its 
masonry, this design could be improved by leaving a weep hole in 
the side walls, 2 or 3 inches wide and the depth of a course of 


* In computing the contents of masonry structures, it is necessary to remember 
that the volume of any mass which is made up of prisms, wedges, and pyramids—or 
cones __ mus t be determined by the prismoidal formula; but if the mass is composed 
wholly of prisms and wedges, the contents can be correctly found by using the aver¬ 
age of the end areas. 

t Published by permission of A. A. Robinson, Chief Engineer. 

X Compare with § 555. 







360 


BRIDGE ABUTMENTS 


[CHAP. XT. 






1 






Fig. 83.—U Abutment.—A. T. & S. F. R. R 


























































































































































U ABUTMENT, 


361 


TABLE 38. 

Quantity of Masonry in U Abutments of the General Form 

shown in Fig. 83. See 8 560. 


1 Height-Top of Footing 
to Bottom of Coping. 

Dimensions of the 
Bottom of the 
Abutment. 

Thickness of the Wing 
at the Bottom. 

Quantity of 
Masonry, ex¬ 
clusive OF 
Coping.* 

Width. 

Thickness. 

Area. 

Head. 

Two Wings, per 
foot of length. 

feet. 

feet. 

feet. 

feet. 

feet. 

cu. ft. 

cu. ft. 

1 

22.2 

5.1 

113 

3.1 

Ill 

6.0 

2 

22.3 

5.2 

115 

3.2 

225 

12.3 

3 

22.5 

5.2 

119 

3.2 

342 

18.8 

4 

22.7 

5.3 

120 

3.3 

462 

25.2 

5 

22.8 

5.4 

124 

3.4 

584 

32.0 

6 

23.0 

5.5 

126 

3.5 

709 

39.0 

7 

23.2 

5.6 

129 

3.6 

837 

46.0 

8 

23.3 

5.7 

132 

3.7 

968 

53.3 

9 

23.5 

5.8 

135 

3.8 

1,101 

60.8 

10 

23 7 

5.8 

138 

4.0 

1.238 

68.4 

11 

23.8 

5.9 

141 

4.4 

1,377 

76.8 

12 

24.0 

6.0 

144 

4.8 

1,520 

86.0 

13 

24.2 

6.1 

147 

5.2 

1,665 

96.0 

14 

24.3 

6.2 

150 

5.6 

1,814 

106.8 

15 

24.5 

6.2 

153 

6.0 

1,966 

118.4 

16 

24.7 

6.3 

156 

6.4 

2,120 

130.8 

17 

24.8 

6.8 

169 

6.8 

2,288 

144.0 

18 

25.0 

7.2 

180 

7.2 

2,478 

158.0 

19 

25.2 

7.6 

191 

7.6 

2; 688 

172.8 

20 

25.3 

8.0 

203 

8.0 

2,920 

188.4 

21 

25.5 

8.4 

214 

8.4 

3,174 

204.8 

22 

25.7 

8.8 

226 

8.8 

3,449 

222.0 

23 

25.8 

9.2 

238 

9.2 

3,746 

240.0 

24 

26.0 

9.6 

250 

9.6 

4,066 

258.8 

25 

26.2 

10.0 

262 

10.0 

4,408 

278.4 

26 

26.3 

10.4 

274 

10.4 

4,772 

298.8 

27 

26.5 

10.8 

286 

10.8 

5,160 

320.0 

28 

26.7 

11.2 

299 

11.2 

5,570 

342.0 

29 

26.8 

11.6 

311 

11.6 

6,003 

364.8 

30 

27.0 

12.0 

324 

12.0 

6,460 

388.4 

31 

27.2 

12.4 

337 

12.4 

6,941 

412.8 

32 

27.3 

12.8 

350 

12.8 

7,445 

438.0 

33 

27.5 

13.2 

363 

13.2 

7,973 

464.0 

34 

27.7 

13.6 

376 

13.6 

8.526 

490.8 

35 

27.8 

14.0 

390 

14.0 

9,103 

518.4 


* For dimensions of coping and pedestal blocks, 
see second paragraph of § 558. 


Examples of the Method of” 
using the Table. 


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Total masonry = (335.4) cu. yds........ = 9,054.7 




























































362 


BKIDGE ABUTMENTS. 


[CHAP. XV. 


masonry, for each 4 or 5 square yards of wing wall. Cinders, or 
sand and gravel are sometimes used to fill in between the wing walls 
to give a better drainage, and also to decrease the lateral thrust of 
the earth. 

560. Contents of U Abutments. The table on page 361 gives 
the contents of U abutments of the form shown in Fig. 83. The 




ric 64 

T ABUTMENT 

^calc of cel 


quantities were computed on the basis that the thickness of the 
walls was four tenths the height, except that no wall was taken of a 
less thickness than that given by the thickness at the top and the 
batter as in the drawing. 

561. T Abutment. Fig. 84 shows the ordinary form of T abut- 





































































T ABUTMENT 


363 


TABLE 39. 

Quantity op Masonry in T Abutments of the General Form 

shown in Fig. 84. See 8 562. 


Height of Abutment- 
Foundation to Coping. 

Dimensions of the 
Bottom of the Head. 

Width. 

Thickness. 

Area. 

feet. 

feet. 

feet. 

feet. 

5 

22.8 

5.8 

133 

6 

23.0 

6.0 

138 

7 

23.2 

6.2 

143 

8 

23 3 

6.3 

148 

9 

23.5 

6.5 

153 

10 

23.7 

6.7 

158 

11 

23.8 

6.8 

163 

12 

24.0 

7.0 

168 

13 

24.2 

7.3, 

173 

14 

24.3 

7.3 

178 

15 

24.5 

7.5 

184 

16 

24.7 

7:7 

189 

17 

24.8 

7.8 

195 

18 I 

25.0 

8.0 

200 

19 

25.2 

8.2 

206 

20 

25.3 

8.3 

211 

■21 

25.5 

8.5 

217 

22 

35.7 

8.7 

222 

23 

25.8 

8.8 

228 

24 

26.0 

9.0 

234 

25 

26.2 

9.2 

240 

26 

26.3 

9.3 

246 

27 

26.5 

9.5 

252 

28 

26.7 

9.7 

258 

29 

26.8 

9.8 

264 

30 

27.0 

10.0 

270 

31 

27.2 

10.2 

276 

32 

27.3 

10.3 

282 

.33 

27.5 

10.5 

289 

34 

27.7 

10.7 

295 

35 

27.8 

10.8 

301 


Quantity of Masonry, 
Exclusive of Coping. 

Head. 

Wedge. 

Tail, per foot of 
length. 

CM. ft. 

CM. ft. 

CM. ft. ; 

607 

12.5 

60 

743 

18.0 

72 

883 

24.5 

84 

1,029 

32.0 

96 

1,179 

40.5 

108 

1,334 

50.0 

120 

1,495 

60.5 

132 

1,660 

72.0 

144 

1,831 

84.5 

156 

2,006 

98.0 

168 

2,188 

112.5 

180 

2,374 

128.0 

192 

2,566 

144.5 

204 

2,763 

162.0 

216 

2,966 

180.5 

228 

3,174 

200.0 

240 

3,388 

220.5 

252 

3,608 

242.0 

264 

3,833 

264.5 

276 

4,064 

288.0 

288 

4,301 

312.5 

300 

4,544 

338.0 

312 

4,793 

364.5 

324 

5,047 

392.0 

336 

5,308 

420.5 

348 

5,575 

450.0 

360 

5,848 

480.5 

372 

6,127 

512.0 

384 

6,413 

544.5 

396 

6,705 

578.0 

408 

7,003 

612.5 

420 


Area of coping on 2 wings, per ft. of length = 5 sq. ft. 

Area of coping on bridge-seat = 138 


Example of the Method of 
using the Table. 






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CO 50 Tf 
CQ ■»—t 

I ° 

& 11 II II II 

.g 

a, 10'^ 

O WMmo 
y XQO000 
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«ISW 

vXXX 

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s 'v L ~ ia . in . 

S 2 00 ” 
§ *xxx 

• O ^ CO 10 
. Sh +3 t—I F-i 

31 O ll ll II 

.sr-s s ^ 

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S-o c-£ 
s _ © w 

8 O ^ 0 ) 

0 ®„ .. 
«o 8 +i^f' 
82 £3 
•38 

§■?<&§ 

£ r4£ 4 J ^ 2 - 

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w fe- - 

© 10 S’* ■* 

^ bJD >■ 

. ao: : 
48 r .0 
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op .5 
W 5 *-. Pc5 

^ r-l O Cg 8 “ 

rfi © ° * 3 
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T)I t-Tj( O « C M O W 
nONOWWWr-t. 
Oi th_ 0* -r-r »£5 © O* 

05 CJ t-I 

II II II II II II II II II 




oo m »n 




06 06 ^ 




xxx 




000 




It QC G> 

Ci tH 




11 11 11 


1C 


-S 



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rH 


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X 


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c 3 

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X «H 

o 


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8® 15 ’ 


oiS.bC-. 

II 00 'S'* 
o? -3 

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2 M *- 

«s || oi 
•5 += ' l_l 

5 cs 0 
JO a; — . 

cc P -* 
A! A a3 
« 

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ag * 3 
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be. - 
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m m 
” , pi c? 

d££ xx 

oiooo wo . 
*■"' CO CO 

i" "Sx 

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ci GO 


# 6p.- 

’I " 


a. 

o- 


3 - 


a 

43. 

-u> . 
03 


13 

cs: 

03 


43 

73- 
fl' 
S3 

bo 

a 


o ; 

830 OT 
.Km £ 


O bc32 <33 ® 

e Sr © EO 
_ .5 © i? ® 2 3 

83 PoS j3 £[2 £^o 
feO^S'Soo 

> O^H PPi C +J<M 


,3 ®„ „ 

u <i3 3 


§ 

OS'S O 
c 


Total masonry = 354.3 cubic yards = 9,567 




























































364 


BRIDGE ABUTMENTS. 


[CHAP. X\- 


ment. For railroad bridges the head is usually not less than 5 ft. 
X 20 ft., nor more than 6 ft. X 22 ft., under the coping, according 
to the size of the bridge. The tail wall is usually 10 or 12 ft. wide, 
and of such length that the foot of the slope of the embankment 
will just reach to the back of the head wall. The batter on the 
head wall is 1 to 12 or 1 to 24 all around. The tail wall is generally 
built vertical on the sides and the end. Notice the batter at the 
top of the free end of the tail wall. This is known as the “frost 
batter,” and is to prevent the frost from dislocating the corner of 
the masonry. The drainage of the ballast pocket should be pro¬ 
vided for by leaving a space between the ends of two stones. 
Formerly the tail wall was sometimes only 7 or 8 feet wide, in which 
case the ties were laid directly upon the masonry without the inter¬ 
vention of ballast; but this practice has been abandoned, as being 
very destructive of both rolling stock and masonry. 

According to the common theories for retaining walls, T abut¬ 
ments with dimensions as above have very large factors of stability 
against sliding, and overturning, and crushing. 

562. Contents of T Abutments. The table on page 363 gives the 
contents of the abutments of the form shown in Fig. 84. The 
height of the tail above the under side of the bridge-seat coping will 
vary with the thickness of the pedestal blocks, and with the style of 
the bridge; and hence the table gives the quantities in the abutment 
below the bridge-seat coping and above the footing. The quantity 
of masonry above this line will vary also with the amount of ballast 
used. The term “wedge” in the table is used to designate that 
part of the tail included between the head and a vertical plane 
through the lower edge of the back face of the head. 

563. Foundation. Usually but little difficulty is encountered 
in securing a foundation for bridge abutments. Frequently the 
foundation is shallow, and can be put down without a coffer-dam, 
or at most with only a light curb (see §§ 316-20). Where the ground 
is soft or liable to scour, a pile foundation and grillage is generally 
employed. For the method of doing this, see Art. 3, Chapter XI ; 
and for examples of this kind of foundation, see Fig. 84 (page 362), 
Fig. 86 (page 380), and Fig. 90 (page 386). 

Where there is no danger of undenvashing, and where the foun¬ 
dation will at all times be under water, the masonry may be started 
upon a timber platform consisting of timbers from, say, 8 to 12. 





QUALITY OF MASONRY. 


365 


inches thick, laid side by side upon sills, and covered by one or 
more layers of timbers or thick planks, according to the depth of 
the foundation and the magnitude of the structure. For an exam¬ 
ple of a foundation of this class, see Plate II. For a discussion of 
the method of failure by sliding on the foundation, see § 491. 

564. Quality of Masonry. —Bridge abutments are built of 
first-class masonry (§ 207) or of second-class (§§ 209 and 212), ac¬ 
cording to the importance of the structure. See also the specifica¬ 
tions for bridge pier masonry (§§ 591-600). The coping should be 
composed of as large stones as practicable—not less than 12 inches 
thick, and 15 or 18 inches thick is better and more frequently used. 

Sometimes, the bed plates of the bridge rest directly upon the 
coping, but usually upon a stone pedestal block (see Figs. 82 and 
83), in which case small pedestals, upon which the rail stringers 
rest (see Fig. 90, page 386), are also generally used. 

565. COST. For data on the cost of masonry, see §§ 232-38. 



CHAPTER XVI. 


BRIDGE PIERS. 

566. The selection of the site of the bridge and the arrangement 
of the spans, although important in themselves, do not properly be¬ 
long to the part of the problem here considered ; therefore they 
will be discussed only briefly. The location of the bridge is usually 
a compromise between the interests of the railroad or highway, and 
of the river. On navigable streams, the location of a bridge, its 
height, position of piers, etc., are subject to the approval of engi¬ 
neers appointed for the purpose by the United States Government. 
The law requires that the bridge shall cross the main channel nearly 
at right angles, and that the abutments shall not contract nor the 
piers obstruct the water way. For the regulations governing the 
various streams, and also reports made on special cases, see the 
various annual reports of the Chief of Engineers, U. S. A., particu¬ 
larly Appendix X 3 , of the Report for 1878. 

The arrangement of the spans is determined mainly by the rela¬ 
tive expense for foundations, and the increased expense per linear 
foot of long spans. Where the piers are low and foundations easily 
secured, with a correspondingly light cost, short spans and an in¬ 
creased number of piers are generally economical, provided the piers 
do not dangerously obstruct the current or the stream is not navi¬ 
gable. On the other hand, where the cost of securing proper foun¬ 
dations is great and much difficulty is likely to be encountered, long 
spans and the minimum number of piers is best. Sound judgment 
and large experience are required in comparing and deciding upon 
the plan best adapted to the varying local conditions. 

Within a few years it has become necessary to build bridge piers 
of very great height, and for economical considerations iron has 
been substituted for stone. The determination of the stability of 
such piers is wholly a question of finding the stress in frame struc¬ 
tures,—the consideration of which is foreign to our subject. 

366 


ART. 1.] 


THEORY OF STABILITY. 


36 ? 


Art. 1. Theory of Stability. 

567. Method OF Failure. A bridge pier may fail in any one 
of three ways : (1) by sliding on any section on account of the ac¬ 
tion of the wind against the train, bridge, and exposed part of the 
pier, and of the current of the stream against the immersed part of 
the pier; or (2) by overturning at any section when the moment of 
the horizontal forces above the section exceeds the moment of the 
weight on the section ; or (3) by crushing at any section under the 
combined weight of the pier, the bridge, and the train. The 
dimensions of piers are seldom determined by the preceding condi¬ 
tions ; the dimensions required at the top (§ 584) for the bridge 
seat, together with a slight batter for appearance, generally give 
sufficient stability against sliding, overturning, and crushing. How¬ 
ever, the method of determining the stability will be briefly out¬ 
lined and illustrated by an example. 

568. Stability against Sliding. Effect of the Wind. The 
pressure of the wind against the truss alone is usually taken at 50 
lbs. per sq. ft. against twice the vertical projection of one truss, 
which for well-proportioned iron trusses will average about 10 sq. ft. 
per linear foot of span. The pressure of the wind against the truss 
and train together is usually taken at 30 lbs. per sq. ft. of truss and 
train. The train exposes about 10 sq. ft. of surface per linear foot. 
The pressure of the wind against any other than a flat surface is 
not known with any certainty ; for a cylinder, it is usually assumed 
that the pressure is two thirds of that against its vertical projection. 

569. Effect of Current. For the pressure of the current of 
water against an obstruction, WeisbaclFs Mechanics of Engineering 
(page 1,030 of Coxe^s edition) gives the formula, 

P = swk^~, .( 1 )' 

in which P is the pressure in pounds, s the exposed surface in 
sq. ft., Tc a co-efficient depending upon the ratio of width to length 
of the pier, w the weight of a cubic foot of water, v the velocity in 
ft. per sec., and g the acceleration of gravity. For piers with 
rectangular cross section, h varies between 1.47 and 1.33, the first 
being for square piers and the latter for those 3 times as long as 





368 


BRIDGE PIERS. 


[CHAP. XVI. 

wide ; for cylinders, h — about 0.73. The law of the variation of 
the velocity with depth is not certainly known; but it is probable 
that the velocity varies as the ordinates of an ellipse, the greatest 
velocity being a little below the surface. Of course, the water has 

its maximum effect when at its highest stage. 

570. Effect of Ice. The pier is also liable to a horizontal press¬ 
ure due to floating ice. The formulas for impact are not applica¬ 
ble to this case. • The assumption is sometimes made that the field 
of ice which may rest against the pier, will simply increase the sur¬ 
face exposed to the pressure of the current. The greatest pressure 
possible will occur when a field of ice, so large that it is not stopped 
by the impact, strikes the pier and plows past, crushing a channel 
through it equal to the greatest width of the pier, ilie lesulting 
horizontal pressure is equal to the area crushed multiplied by the 
crushing strength of the ice. The latter varies with the tempera¬ 
ture; but since ice will move down stream in fields only when 
melting, we desire its minimum strength. The crushing strength 
of floating ice is sometimes put at 20 tons per sq. ft. (300 lbs. per 
sq. inch); but in computing the stability of the piers of the St. 
Louis steel-arch bridge, it was taken at 600 lbs. per sq. inch (43 
tons per sq. ft.). According to experiments made under the 
author’s direction,* the crushing strength of ice at 23° F., varies 
between 370 and 760 lbs. per sq. in. 

Occasionally a gorge of ice may form between the piers, and 
dam the water back. The resulting horizontal pressure on a pier 
will then be equal to the hydrostatic pressure on the width of the 
pier and half the span on either side, due to the difference between 
the level of the water immediately above and below the bridge 
opening. A pier is also liable to blows from rafts, boats, etc.; but 
as these can not occur simultaneously with a field of ice, and will 
probably be smaller than that, it will not generally be necessary to 
consider them. 

A lateral pressure on the pier is possible, due to the earth’s be¬ 
ing washed away from one side and not from the opposite. It will 
be on the safe side, and near enough for this purpose, to assume 
that this effect is equal to the pressure of a liquid whose density is 
the difference between that of the water and the saturated soil dis¬ 
placed. Under these conditions, the actual tendency to slide is 

* The Technograph, University of Illinois, No. 9 (1894-95), pp. 38-48. 








THEORY OF STABILITY. 


369 


ART. l.'j 

'equal to the square root of the sum of the down stream forces and 
the lateral thrust. However, this refinement is unnecessary, par¬ 
ticularly since a pier which is reasonably safe against overturning 
and crushing will be amply safe against sliding. 

571. Resisting Forces. The resisting force is the friction due to 
the combined weight of the train, bridge, and the part of the pier 
above the section considered. For the greatest refinement, it would 
be necessary to compute the forces tending to slide the pier for two 
conditions : viz., (1) with a wind of 50 lbs. per sq. ft. on truss and 
pier, in which case the weight of the train should be omitted from 
the resisting forces ; and (2) with a wind of 30 lbs. per sq. ft. on 
truss, train, and pier, in which case the weight of a train of empty 
box cars should be included in the resisting forces. For a table of 
weights of masonry, see page 200. If the water can find its way 
under the foundation in thin sheets, the weight of the part of the 
pier that is immersed in the water will be diminished by 62|- lbs. 
per cu. ft. by buoyancy ; but if it finds its way under any section 
by absorption only, then no allowance need be made for buoyancy. 

The resisting force is equal to the product of the total weight 
and the co-efficient of friction. For values of the co-efficient of 
friction, see the table on page 315. The tenacity of the mortar is 
usually neglected, although it is a very considerable element of 
strength (see § 137). 

572. Stability against Overturning. The forces which tend 
to produce sliding also tend to produce overturning, and the forces 
which resist sliding also resist overturning ; hence, there remains to 
determine only their points of application. The stability can be 
determined either by moments or by resolution, as was explained for 
dams ; but in this case, it is easier by moments, since there are sev¬ 
eral horizontal forces, and it requires considerable work to find their 
resultant as demanded by the method by resolution of forces. 

573. A. By Moments. By this method, it is necessary to find 
the arm of the forces, i. e,, the perpendicular distance from the line 
of action of the forces to a point about which the pier tends to turn. 
This is the same method as that used in §§ 493-98, which see. 

The center of pressure of the wind on the truss is practically at 
the middle of its height; that of the wind on the train is 7 to 9 
feet above the top of the rail ; and that of the wind on the pier is 
at the middle of the exposed part. The arm for the pressure of the 







370 


BRIDGE PIERS. 


[CHAP. XT!- 


ice should be measured from high water. The center of pressure 
of the current is not easily determined, s : nce the law of the varia¬ 
tion of the velocity with the depth is not known ; but it will proba¬ 
bly be safe to take it at one third the depth. Finally, the downward 
forces will usually act vertically through the center of the pier. 

From these data the overturning and resisting moments can 
easily be computed. For equilibrium, the summation of the former 
must be less than the latter. The above principles will be further 
elucidated in §§ 579-80 by an example. 

574. B. By Resolution of Forces. This is the method explained 
in § 499 (page 320). In that case the problem was very sim¬ 
ple, since there were but two forces ; but in the present case there 
are several horizontal forces and also several vertical ones. The first 
step is to find a single force which is equivalent in every respect to 
the combined effect of all the horizontal forces; the second is to 
find an equivalent for all of the vertical forces ; and the third is to 
find the resultant of these two forces. 

The horizontal distance, x, of the point of application of the re¬ 
sultant of all the vertical forces, back from the toe of the pier, is 
found by the equation. 


_ sum of the moments of the vertical forces 
sum of the vertical forces 


( 2 ) 


The weight of the train and bridge act vertically through the center 
of the pier ; and if the pier is symmetrical, as it usually is, the 
weight of the pier will also act through its center. Therefore, x in 
equation (2) will usually be half the length of the pier. 

The vertical distance, y , of the point of application of the re¬ 
sultant of all the horizontal forces above any horizontal joint is 
found by the equation, 


V = 


_ sum of the moments of the horizontal forces 


sum of the horizontal forces 


( 3 ) 


Having found x and y, as above, draw a vertical line at a distance 
x back from the down stream end of the pier; on this line lay off a 
distance y above the horizontal joint under consideration. The 
point thus determined corresponds to a of Fig. 70 (page 320). Con¬ 
struct the parallelogram of forces by laying off, to any convenient 







ART. 1.1 


THEORY OF STABILITY. 


371 


scale, (1) a horizontal line equal to the sum of all the horizontal 
forces acting on the pier, and (2) a vertical line equal to the sum of 
all the vertical forces ; and complete the diagram by drawing the 
resultant. The stability of the pier is determined by the ratio of 
A G to N C, Fig. 70. 

575. Stability against Crushing. Represent the maximum 
pressure by P, the total weight on the section by W, the area of the 
section by S, the moment of inertia of the section by /, the length 
of the section by l, and the overturning moment by M ; then from 
equation (1), page 205, we have 


Jf 

S~ 


Ml 

YJ 



For the particular case in which the pier has a rectangular horizon¬ 
tal cross section, the above formula becomes the same as equation 
(18), (page 322,) as deduced for an element of a masonry dam. 

The method of applying the above equation will be explained in 
§ 581 by an example. 

576. Example of Method of Computing Stability. Fig. 85 

shows the dimensions of the channel pier of the Illinois Central R. 
R. bridge over the Ohio River at Cairo, Ill. This pier stands be¬ 
tween two 523-foot spans. Its stability will now be tested by the 
preceding principles. 

577. Stability against Sliding. We will examine the stabil¬ 
ity against sliding on the top footing course. The wind surface of 
the truss = 10 sq. ft. X 523 = 5,230 sq. ft. The wind pressure 
against the truss at 30 lbs. per sq. ft. = 30 lbs. X 5,230 =150,900 
lbs. = 78 tons ; and the wind pressure on the truss at 50 lbs. = 
50 lbs. X 5,230 = 261,500 lbs. = 131 tons. 

The wind pressure on train at 30 lbs. per sq. ft. = 30 lbs. X 
523 X 10 = 156,900 lbs = 78 tons. 

The pressure of the wind against a section of the pier 52 ft. 
long, is 20 lbs. X 52 X 14 = 14,560 lbs. = 7 tons. 

The pressure due to the ice is found as follows: Assume the 
thickness to be 1 foot, and also assume the crushing strength of 
ice to be 200 lbs. per sq. in. =, say, 15 tons per sq. ft. The pier is 
16 ft. wide at the high-water line. Hence the resistance required in 
the pier to crush its way through a field of ice is 15 tons X 16 X 1 
= 240 tons. 






372 


BRIDGE PIERS 


[CHAP. XVI 





Fig. 85. —Channel Pier, Cairo Bridge. 















































AET. l.J 


THEOEY OF STABILITY. 


373 


The pressure clue to the current is found as follows: From 

2 

V 

§ 569, P = sivk —. s represents the exposed surface = 70 ft. X 

19 ft. = 1,330 sq. ft., which value is equivalent to assuming that 
the river may scour to the top of the footing courses, k represents 
a co-efficient, which, if the pier were rectangular, would be about 
1.4, and if the pier were cylindrical would equal about 0.73. We 
will assume it to be 1 . 1 , —a trifle more than the mean of these two 
values, w = 62.5 lbs. per cu. ft. The surface velocity at the 
bridge site was measured* “ when the Mississippi and the Ohio 
were at about the same stage,” and found to be 4 miles per hour 
(— 6 ft. per second); but as high water may occur in the Ohio at 
the time of moderately low water in the Mississippi, the possible 
maximum velocity is greater than the above, and hence we will as¬ 
sume that it is 10 ft. per second. The velocity of the water at 
various depths below the surface of a stream varies as the ordinate 
of an ellipse; but the effect of the mean velocity is approximated 
with sufficient accuracy for this purpose by assuming that the mean 
pressure is half of that due to the surface velocity. Substituting 
these numbers, the above equation becomes P — 1,330 X 1.1 X 
62.5 X VY = 70.5 tons = 70 tons with sufficient accuracy. Divid¬ 
ing this by 2 to get the pressure corresponding to the mean velocity, 
we have the pressure of the current equal to 35 tons. 

Collecting the preceding results, we have: 


Wind on truss,. 78 tons. 

“ “ train,.78 “ 

“ “ pier,. 7 “ 

Pressure of ice, .. 240 “ 

“ “ water,.35 “ 


Total force tending to slide the pier on the foot¬ 
ing .— 438 tons. 


578. The weight of the bridge will be assumed at 2 tons per 
lineal foot; and hence the total weight is 2 tons X 523 = 1,046 
tons. 

The weight of a train of empty cars is about 0.5 ton per lineal 


* Third Annual Report of the Illinois Society of Engineers, p. 78. 
















374 


BRIDGE PIERS. 


[CHAP. XVI. 


foot; and hence the total weight of the train is 0.5 tons X 523 =- 
261 tons. 

The amount of masonry below the high-water line = 67,946 cu. 
ft.; the amount above the high water line = 24,534 cu. ft.; and 
hence the total masonry = 92,480 cu. ft. We will assume the 
weight of the masonry to be 150 lbs. per cubic foot. Then the 
weight of the masonry is 150 lbs. X 92,480 = 6,936 tons. 


Collecting these results, we have: 

Weight of the bridge,. 1,046 tons. 

“ “ “ train of empty cars,. 261 “ 

“ “ “ masonry,. 6,936 “ 

Total weight to resist sliding.= 8,243 tons. 


Sliding cannot take place, if the co-efficient of friction is equal 
to or greater than 438 -4- 8,243 = 0.053. For values of the co-ef¬ 
ficients of friction, see the table on page 315. In the above ex¬ 
ample, the factor of safety against sliding is at least 12 to 15. 

579. Stability against Overturning. 'We will consider the 
stability against overturning about the top of the upper footing 
course. The wind on the truss = 78 tons; the ^rm of this force = 
height of the pier (123 ft.) -f- half the depth of the truss (30 ft.) = 
153 ft.; and therefore the moment of this force = 78 tons X 153 
ft. = 11,934 foot-tons. 

The pressure of the wind on the train = 78 tons; and the arm 
of this pressure = distance from footing to top of pier (123 ft.) -f- 
distance from top of pier to top of rail (8 ft.) -f- distance from top 
of rail to center of train (8 ft.) = 139 ft. Therefore the moment 
of this pressure is 78 tons X 139 ft. = 10,842 foot-tons. 

The pressure of the wind against the pier is 7 tons (§ 577); the 
arm of this force = \ (202 -j- 150) — 79 = 97 ft.; and the moment of 
this force = 679 foot-tons. 

The pressure of the ice is 240 tons, the arm is 70 ft., and the 
moment is 16,800 foot-tons. 

The pressure of the water is 35 tons. The center of pressure 
lies somewhere between one third and one half of the depth from 
the top; and as the increased area at the base of the pier compen¬ 
sates in part for the decrease of velocity with the depth, we will as¬ 
sume that it is at half the depth. The arm then is 36 ft., and the 
moment is 35 tons X 36 ft. = 1,260 foot-tons. 







ART. 1.] 


THEORY OF STABILITY. 


375 


Collecting these results, we have: 
Moment of the wind on the truss, 


it 

a 

it 

<c 


a a 

a i c 

a 

a 


( c 

cc 


a (< 
i ( i c 


train, 
pier, . . 

“ pressure of the ice, . 

current 


. 11,934 foot-tons. 
. 10,842 

679 ' “ 

. 16,800 
. 1,260 


Total overturning moment.= 41,515 foot-tons. 

580. The total weight above the joint considered is (§ 578) 

8,243 tons. This force acts vertically down through the center of 
the pier; hence the arm is 31.5 ft., and the total moment resisting 
overturning is 8,243 x 31.5 = 259,654 foot-tons. The factor of 
safety against overturning about the top of the upper footing 
course is 259,654 -4- 41,515 = 6.3. v 

Assuming the train to be oft the bridge, and that the wind 
pressure on the truss is 50 lbs. per sq. ft., and following the method 
pursued above, it is found that the factor of safety against over¬ 
turning these conditions is 6.4. 

581. Stability against Crushing. The maximum pressure on 
the section will occur when the loaded train is on the bridge and 
all the horizontal forces are acting with their full intensity. The 
load when an empty train is on the bridge is (§ 578) 8,243 tons. 
Assuming that a loaded train will weigh 1J tons per lineal foot, we 
must add (0.75 tons X 523 =) 392 tons to the above for the 
difference between a loaded and an unloaded train. Then the total 
direct pressure is 8,243 + 392 = 8,635 tons. The area of the sec¬ 
tion at the top of the footing course is 1,160 sq. ft. Hence, the 
maximum direct pressure is 8,635 -4- 1,160 = 7.4 tons per sq. ft. 

The moment to overturn, M, = 41,515 foot-tons. The greatest 
length of the section = 63 ft. The moment of inertia of the sec¬ 
tion about an axis through its center and perpendicular to its 
length = 287,917 (ft.). From § 575, the maximum pressure 

P-IZ 1 

S ‘ 2i* 

Substituting the above quantities in this equation gives 

p — 7.4 -U 41,515 X 63 7.4 4 - 4.5 = 41,9 tons per sq. ft. 

* * ‘ 2 X 287,917 R 4 

Since it is highly improbable that all the forces will act at the 
same time with the intensity assumed in the preceding computa- 





376 


BRIDGE PIERS. 


[CHAP. XVI- 


tions, we may conclude that the pressure will never exceed 11.9 
tons per sq. ft. A comparison of this with the values of the com- 
pressive strength of masonry as given in § 222 (page 149) shows 
that this pressure is entirely safe. 

Since this is an unusually high pier under an unusually long 
span, and since the overturning and resisting moments and also the 
top dimensions of the pier vary with the span, we may draw the 
conclusion that any pier which has sufficient room on top for the 
bridge seat (§ 584) and which has a batter of 1 in 12, or 1 in 24, is 
safe against any mode of failure. 

582. Pressure on the Bed of the Foundation. The caisson 
is 70 feet long, 30 feet wide, and 50 feet high. The load 
on the base is equal to the weight on the top of the footing plus 
the weight of the footings plus the weight of the caisson. 
The weight above the footing = 8,635 tons (§ 581). The weight 
of the footings = 1,300 sq. ft. X 4 ft. X 150 lbs. = 390 tons. The 
weight of the caisson = 70 ft. X 30 ft. X 50 ft. X 100 lbs. = 5,250 
tons. The total weight on the bed = 8,635 -j- 390 4- 5,250 = 14,- 
275 tons. The area = 70 ft. x 30 ft. = 2,100 sq. ft. The direct 
pressure per unit of area = 14,275 -4- 2,100 = 6.8 tons per sq. ft. 

The overturning moment, M, is equal to the moment about the 
top of the footing (§ 581) plus the product of the sum of the hori¬ 
zontal forces and the distance from the footing to the base of the 
caisson; or, the moment about the base = 41,515 foot-tons -f- 438 
tons X 54 ft. = 65,167 foot-tons. The moment of inertia, 1 , = 
T b- 30 (70) 3 = 857,500 (ft.). I = 70 ft. The concentrated pressure 
caused by the tendency to overturn is 

M l 65,167 X 70 _ „ , 

2 / “ 2 X 857,500 2 ' ‘ tonS ‘ 

The caisson was sunk all the way through, and rests, on sand ; 
consequently the water will find its way freely under the entire 
foundation, thus causing buoyancy to act with its full force. This 
upward force of the water will be equal to the volume of the im¬ 
mersed masonry multiplied by the weight of a cubic foot of w T ater; 
or the buoyancy = (67,946 -f- 5,200 -f- 105,000) X 62.4 = 5,558 tons. 
The lifting effect of buoyancy is (5,558 -4- 2,100 =) 2.62 tons per 
sq. ft. 

Therefore, the total pressure is not greater than 6.8 + 2.7 — 2.6- 
= 6.9 tons per sq. ft. 






ART. 2.] 


DETAILS OF CONSTRUCTION. 


377 


The pressure would never be so much, for the following reasons : 
1 . There is no probability that both spans will be covered by a train 
of maximum weight at the same time that the maximum effects of 
the wind, of the current, and of the ice occur. 2. The friction on 
the sides of the caisson will sustain part of the load. A friction of 
600 lbs. per sq. ft., which was about the amount experienced in 
sinking these piers (see § 455), would decrease this pressure about 
1 J tons per sq. ft. 

Therefore., we conclude that the pressure on the sand will be at 
least as much as 6.8 — 1.5 — 2.6 = 2.7 tons per sq. ft.; and that it 
may possibly, but not probably, amount to 6.8 -f- 2.7 — 2.6 — 1.5 = 
5.4 tons per sq. ft. The larger value was taken at the greatest pos¬ 
sible one for the sake of establishing the conclusion stated in the 
last paragraph of § 581. 

583. Oilier Examples . At the St. Louis steel-arch bridge 
the greatest pressure possible on the deepest foundation (bed¬ 
rock) is 19 tons per sq. ft. The pressure at the base of the 
New York tower of the East River suspension bridge is about 

tons per sq. ft. upon a stratum of sand 2 feet thick overlying 
bed-rock ; and at the base of the masonry the pressure is about 11 -J 
tons per sq. ft.* The corresponding quantities for the Brooklyn 
tower were a little over a ton less in each case. At the Plattsmouth 
bridge f the maximum pressure caused by the weight of train, bridge, 
and pier is 3 tons per sq. ft. At the Bismarck bridge f the pressure 
due to the direct weight is 3 tons per sq. ft. on clay. 

Art. 2. Details of Construction. 

584. Top Dimensions. The dimensions on the top will depend 
somewhat upon the form of the cross section of the pier, and also 
upon the style and span of the bridge; but, in a general way, it may 
be stated that, for trussed spans of 100 ft. or over, the dimensions 
under the coping will not be less than 5 ft. X 20 ft.; for 250-ft. 
spans, 8 ft. X 30 ft.; and for 500-ft. spans, 10 ft. X 40 ft. Appar¬ 
ently 6 ft. X 22 ft. under the coping is the favorite size for spans of 
100 to 200 ft. 


* F. Collingwood, assistant engineer, in Van Nostrand’s Engin’g Mag., vol- xvi. 
p. 431. 

t Report of Geo. S. Morison, chief engineer. 





378 


BRIDGE PIERS. 


[CHAP. XVI. 


585. Bottom Dimensions. Theoretically the dimensions at the 
bottom are determined by the area necessary for stability; but the 
top dimensions required for the bridge seat, together with a slight 
batter for the sake of appearance, gives sufficient stability (§ 581). 
Only high piers for short spans—a combination not likely to occur 
in practice—are liable to fail by overturning or crushing. 

586. Batter. The usual batter is 1 inch to a foot, although -J- 
an inch to a foot is very common. In high piers it is customary to 
use a batter of 1 to 24, and offset the masonry and introduce a water- 
table at the high-water line, so as to give an average batter of about 
1 to 12. This construction very much improves the appearance, 
and does not add materially to the cost. 

A corbel course, or “belt course,” is sometimes introduced im¬ 
mediately under the coping for appearance’s sake. For an exam¬ 
ple, see Fig. 85 (page 372), Fig. 87 (page 383), and Fig. 88 (page 
384). 

587. Cross Section. The up-stream end of a pier, and to a 
considerable extent the down-stream end also, should be rounded 
or pointed to serve as a cut-water to turn the current aside and to 
prevent the formation of whirls which act upon the bed of the 
stream around the foundation, and also to prevent shock from ice, 
logs, boats, etc. In some respects the semi-ellipse is the best form 
for the ends ; but as it is more expensive to form, the ends are 
usually finished to intersecting arcs of circles (see Figs. 85, 87, and 
89—pages 372, 383, and 385, respectively), or with semi-circulai 
ends. Above the high-water line a rectangular cross section is as 
good as a curved outline, except possibly for appearance. 

A cheaper, but not quite as efficient, construction is to form the 
two ends, called starlings, of two inclined planes. As seen in 
plan, the sides of the starlings usually make an angle of about 45° 
with the sides of the pier (see Fig. 90, page 386). A still cheaper 
construction, and the one most common for the smaller piers, is to 
finish the up-stream end, below the high-water line, with two in¬ 
clined planes which intersect each other in a line having a batter of 
from 3 to 9 inches per foot, and build the other three sides and the 
part of the up-stream face above the high-water line with a batter 
of 1 in 12 or 1 in 24. Of course the simplest construction is to 
make the pier rectangular in horizontal cross sections and give it the 
same batter on all faces. 




ART. 2.] 


DETAILS OF CONSTRUCTION. 


379 


Occasionally, for economy, piers, particularly pivot piers, are 
built hollow—sometimes with and sometimes without interior cross 
walls (see Fig. 86, page 380). The piers of the bridge across the 
Missouri River at Glasgow, Mo., are solid up to the high-water line, 
and above that each pier consists of two stone columns. The piers 
of the bridge over the Missouri at St. Charles, Mo., have a somewhat 
similar construction, except that the secondary piers are connected 
by a comparatively thin wall. 

With piers subjected to a severe pressure from ice, it is customary 
to protect the edge of the nose with an angle-iron or a railroad rail. 

588. Pivot Piers. These differ from the ordinary piers only 
in that they are circular, are larger on top, and have plumb sides. 
Pivot piers are about 25 to 30 feet in diameter, under the coping, 
for spans of 250 to 350 feet, respectively. 

Fig. 86 shows the pivot pier for the Northern Pacific R. R. 
bridge over the Red River at Grand Forks, Dakota. The specifica¬ 
tions for the grillage were as follows: “Fasten the first course of 
timbers together with ^-inch X 20-inch drift bolts, 18 inches apart; 
fasten second course to first course with drift bolts of same size at 
every other intersection. Timbers to be laid with broken joints. 
Put on top course of 4-inch X 12-inch plank, nailed every 2 feet 
with T 7 ¥ -inch X 8 -inch boat spikes. The last course is to be thor- • 
oughly calked with oakum.” 

Pivot piers are protected from the pressure of ice and from 
shock by boats, etc., by an ice breaker which is entirely distinct 
from the pier. The ice breaker is usually constructed by driving a 
group of 60 or 70 piles in the form of a V (the sharp end up stream), 
at a short distance above the pier. On and above these piles a 
strong timber crib-work is framed so as to form an inclined ridge 
up which the cakes of ice slide and break in two of their own weight. 
Between the ice breaker and the pier two rows of piles are driven, 
on which a comparatively light crib is constructed for the greater 
security of the pier and also for the protection of the river craft. 

589. Quality OF Masonry. Bridge piers are usually quarry¬ 
faced ashlar, i. e., first-class masonry (see § 207) backed with rubble. 
Good concrete, if made with reasonable care, is equally as good as 
ordinary rubble masonry, and is sometimes cheaper,—since it affords 
an opportunity to use up the refuse from the quarry. 



in rg n W n 

Fig. 86.—Pivot Pier, Grand Forks Bridge. 


380 


BRIDGE PIERS. 


[CHAP. XVI. 
































































































































DETAILS OF CONSTRUCTION 


381 


ART. 2.] 

For an illustrated description of the method of building concrete 
bridge piers, see Engineering Neivs, yol. xix. pp. 443-44. 

590. Specifications. The following specifications for the ma¬ 
sonry of the railroad bridge over the Missouri River near Sibley, Mo., 
(Octave Chanute, engineer) may be taken as an example of the best 
practice.* 

591. General Requirements. “ The stone to be used in these piers must be 
of what is known as the best quality of Cottonwood limestone, or other stone 
which, in the opinion of the engineer, is of equally good quality and in every 
way suitable for the purpose for which it is to be used. It must be sound and 
durable, free from all drys, shakes, or flaws of any kind whatever, and must 
be of such a character as will, in the opinion of the engineer, withstand the 
action of the weather. No stone of an inferior quality will be accepted or 
even permitted to be delivered upon the ground. The masonry in the bridge 
piers must be of the best and largest stones that the quarry will afford, and 
must be quarried in time to season against frost before being used. 

“ The face stones composing the starling, and the ends and sides of the river 
piers from the neat line about low water up for a distance of twelve (12) feet, 
and also the pedestal blocks of the main piers will be of Minnesota granite, 
or a granite of equal quality approved by the engineer. 

“ All masonry of the main piers shall be regular coursed ashlar of the best 
description, and must be laid in mortar of the proportions of sand and cement 
aereinafter specified. 

“ All stones must be so shaped that the bearing beds shall be parallel to the 
natural beds, and be prepared by dressing and hammering before they are 
brought on the walls, as tooling and hammering will not be allowed after the 
stones are in place. They are to be laid to a firm bearing on their natural beds 
in a full bed of mortar, without the use of chips, pinners, or levelers. No 
shelving projections will be allowed to extend beyond the under bed on either 
side. The stone and work are to be kept free from all dirt that will interfere 
with the adhesion of mortar. Stones must be sprinkled with water before 
being placed in position on the wall. In laying stone in mortar, their beds are 
to be so prepared that when settled down they may rest close and full on the 
mortar. In handling the stones care must be used not to injure the joints of 
those already laid; and in case a stone is moved after being set and the joint 
broken, it must be taken out, the mortar thoroughly cleaned from the beds, 
and then reset. 

“ Wherever the engineer shall so require, stones shall have one or two 14- 
inch iron dowels passing through them and into the stones below. The holes, 
for the dowels shall be drilled through such stones before they are put in 
position on the walls. After the stones are in place the holes shall be con¬ 
tinued down into the under stones at least six (6) inches ; the dowel pins will 
then be set in and the holes filled with neat cement grout. Cramps binding 


* For specifications foi first-class masonry, see § 207; see also Appendix I. 







BRIDGE PIERS. 


[CHAP. XVI. 


382 


the several stones of a course together may be inserted when required by the 
engineer ; in such case they will be counter-sunk into the stones which they 
fasten together. 

592. Face Stones. “ The face stones must be accurately squared, jointed, 
and dressed on their beds and builds ; and the joints must be dressed back at 
least twelve inches (12) from the face. Face stones are to be brought to a joint, 
when laid, of not more than three quarters (f) of an inch nor less than one 
half (|) inch. The courses shall not be less than eighteen (18) inches in thick¬ 
ness, decreasing from bottom to top of the wall. Courses to be well bonded. 
The face stones shall break joints at least twelve (12) inches. The face stones 
may be left rough, except the stones forming the starling, which must be care¬ 
fully dressed to a uniform surface. The edges of face stones shall be pitched 
true and full to line, and on corners of all piers a chisel draft one and a half 
(1|) inches must be carried up from base to the under side of the coping. No 
projection of more than three (3) inches from the edge of face stones will be 
allowed. No stone with a hollow face will be allowed in the work. 

593. Stretchers. “Each stretcher shall have at least twenty (20) inches 
width of bed for all courses of from eighteen (18) to twenty (20) inches rise, 
and for all thicker courses at least as much bed as rise ; and shall have an 
average length of at least three and one half (3|) feet, and no stretcher shall be 
less than three (3) feet in length. 

594. Headers. “Each header shall have a width of not less than eighteen 
inches (18) and shall hold, back into the heart of the wall, the size that it shows 
on the face. The headers shall occupy at least one fifth (A) of the whole face 
of the wall, and be, as nearly as practicable, evenly distributed over it, and be 
so placed that the headers in each course shall divide equally, or nearly so, the 
spaces between the headers in the course directly below. In walls over six 
feet (6) in thickness, the headers shall in no case be less than three and one half 
feet (3i) long; and in walls over nine (9) feet thick, the headers shall be equal 
in length to one third the thickness of the wall, except when this length of 
header exceeds six (6) feet,—no header over six (6) feet long being required. 

595. Backing. “ The headers must alternate front and back, and their 
binding effect be carried through the wall by intermediate stones—not less in 
length and thickness than the headers of the same course—laid crosswise in 
the interior of the wall. The stretchers and all stones in the heart of the wall 
shall be of the same general dimensions and proportions as the face stones, 
and shall have equally good bed and bond, but may have less nice vertical 
joints,—although no space greater than five (5) inches in width shall be left be¬ 
tween stones. All stones in the backing must be well fitted to their places, 
and carry the course evenly quite through the wall. 

596. Coping. “ The tops of the bridge piers, cap stones of the pedestals, 
and such other parts of the masonry as the engineer shall direct, shall be cov¬ 
ered with coping of such dimensions as prescribed. All coping stones shall 
be neatly bush-liammer dressed on the face, bed, top, and joints; and shall be 
well and carefully set on the walls, brought to one quarter (£) inclrjoints, and, 




ART. 2.] 


DETAILS OF CONSTRUCTION 


388 




Fig. 87. —Shore Pter, Blair Bridge 



































































































































































































384 


BRIDGE PIERS. 


[CHAP. XVI. 


if required, be doweled, the dowels being well secured in and to the coping 
with grout. No coping stone shall be less than nine (9) square feet on top. 

597. Pointing. “ All masonry is to be pointed so as to fill the joints solid. 
The surface of the wall is to be scraped clean and the joints freed of all loose 
mortar and refilled solid by using proper ramming tools. Joints must be well 
wet before being pointed. Mortar used in pointing is to be composed of one 
part Portland cement and one part sand. 

598. Cement. “ The cement used in the work shall be equal in quality to 
the best brands of Milwaukee or Louisville cement, and shall be ground so 
that at least 90 per cent, in weight will pass a standard sieve of 2,500 meshes 
to the square inch, and shall have a tensile strength—after being exposed one 
hour, or until set, in air, and the balance of the twenty-four hours in water not 



/S'cule 

——i— —————-— . 11 i » 

/ y 8 12 . 16 

uF 7 <2<2-£- 



below 60° F.—of at least 40 pounds per square inch; and, after being exposed 
one day in air and six days in water, from 60 to 100 pounds per square inch. 

“ All cements shall be furnished by the contractor subject to approval by 
the engineer. The contractor shall provide a suitable building for storing the 
cement, in which the same must be placed before being tested. The engineer 
shall be notified of the receipt of cement at least three days before it is required 
for use, and the inspector may take a sample from each package for testing. 

599. Mortar. “ The mortar shall be composed of the above cement and 
clean, dry, sharp sand in the proportion of one part cement to two parts of 
sand by weight.* The sand and cement shall be thoroughly mixed dry, and, 
after adding sufficient water to render the mass plastic, shall be mixed and 
worked until of uniform consistency throughout. 

“ Mortar remaining unused so long as to have taken an initial set shall not 
be used in the work. 


* This is an unusual, but exact, method of specifying proportions; they are 
usually stated in volumes. 

































































ART. 2 .] 


DETAILS OF CONSTRUCTION. 


385 


600. Pedestal Masonry. “ The pedestals shall be founded upon a bed of 
concrete or upon piles, as may be directed by the engineer. The masonry in 


the pedestals shall be of the best de¬ 
scription of coursed ashlar composed of 
the limestone and the mortar described 
above, the stones to be not less than 
twelve (12) inches thick, and to have 
horizontal beds and vertical joints on 
the face. When the walls do not ex¬ 
ceed three and one half (3£) feet in 
thickness, the headers shall run entirely 
through, or a single stone—square and 
of the proper thickness—may be used. 
In walls over three and one half (31) 
feet in thickness, and not over seven 
<7) feet in thickness, headers and 
stretchers shall alternate, and there 
shall be as many headers as stretchers. 
The space in the interior of the walls 
shall be tilled with a single stone cut 
to tit such space, and said stone shall 
be of the same height as the headers 
and stretchers of the course. In all the 
masonry of these pedestals the slope 
must be carried up by steps and in ac¬ 
cordance with the plans of the engineer. 
All the quoins must have hammer- 
dressed beds, builds, and joints, and 
draft corners.” 

601. Examples of Bridge 
Piers. Fig. 85 (page 372) shows 
the channel pier of the Illinois 
Central R. R. bridge over the 
Ohio at Cairo, Ill. 

Fig. 86 (page 380) shows the 
pivot pier of the Northern Pacific 
R. R. bridge over the Red River 
at Grand Forks, Dakota. 

Fig. 87 (page 383) shows one 
of the two shore piers' of the 
bridge over the Missouri River, 
near Blair, Neb.* This pier sta 



* From the Report of Geo. S. Morison, chief engineer of the bridge. 


Fig. 89.—A Course of a Pier of Cairo Bridge. 




































































386 


BRIDGE PIERS 


[CHAP. XVI, 




Fig. 90.— Pier of St. Croix River Bridge. 













































































































































































































































ART. 2.] 


DETAILS OF CONSTRUCTION. 


387 


“ The vertical joints are shown as they actually are in the struct¬ 
ure.” The masonry is 145 ft. from top to bottom. 

Fig. 88 (page 384) shows the top of the pier between two 525-ft. 
channel spans of the Louisville and Nashville R. R. bridge across 
the Ohio River at Henderson, Ky. 

Fig. 89 (page 385) shows the actual arrangement of the stones in 
one of the courses of one of the channel piers (Fig. 85) of the Illinois 
Central R. R. bridge over the Ohio River, at Cairo, Ill. 

602. Fig. 90 (page 386) shows the river pier of the Chicago, Bur¬ 
lington and Northern R. R. bridge across the.St. Croix River. This 
pier stands between a draw of 370 feet and a fixed span of 153 feet. 
The thickness of the courses is as follows, in order from the bottom 
up : Two courses, including the footing, 28 inches; two 26 inches 
one each 24, 22, 21, 19, and 17 inches ; two 15 inches; four 14 
inches ; one 13 inches ; one 12 inches ; and the coping 18 inches. 

The following table gives the quantity of masonry in the pier and 
illustrates the manner of computing the contents of such structures. 
Notice that the order in the table is the same as that in the pier : 
i. e., the top line of the table relates to the uppermost masonry, etc. 

TABLE 40. 

Contents of the Pier shown in Fig. 90 (page 386). 


Description. 


* 


Dimensions. 


Cubic 

Feet. 


Stringer Rests.. 
Bridge Seats.... 
Coping. 

Neat Work. 

a << 


2 X 2.75' X 8.0' X 3.13'. 

2 X 2.75' X 3.0' X 1.46'. 

7.5' X 24.0' X 1.5'. 

25 17' 

{(2 X 6.5' + 8.6') 23' + (2 X 8.6' + 6.5') 25.1'} —jp .. 

18 17' 

(2 X 8.6'+ 7.1') 3.8' X—. 


Ice Breaker.... 

€ i €i 

Footing Course. 

n n 


(3.6' X 3.6 )(“• + 1.0').. 

4(3.6' X 3.6'+ 4.3' X 4.3') 18.17'. 

9.6' X 29.4' X 2.33'. 

4.8' X 4.8' X 2.33'. 

Total = 230.39 cubic yards = 


51.6 

24.1 

270.0 

4,579.7 

279.6 


17.3 

285.8 

658.5 

53.8 

6,220.4 


603. Iron Tubular Piers. For a description of an iron tubular 
pier, see § 415 ; and for a description of a pier founded upon screw 
piles, see Engineering News, vol. xiii. pp. 210—12. 






























388 


BRIDGE PIERS. 


[CHAP. XYI. 


604. Timber Barrel Piers. The Chicago, Burlington and Quincy 
R. R. has constructed a few “ barrel piers” as an experiment, the 
object being to reduce the cost of foundations, and also to find some 
cheap substitute for masonry. The barrels are cylindrical, 8 feet in 
diameter, and 20 to 30 feet in length. The staves are 10 inches 
thick, 8 inches wide on the outside, and are dressed to fit together 
to form a cylinder. The staves are bolted at the top and bottom 
to two inside rings made of I-beams, and are further held in place 
by strong outside hoops of iron. These caissons or barrels are sunk 
by excavating the soil from the inside. The bottom and top por¬ 
tions of the caisson are filled with concrete, and the intermediate 
portion with sand. On top of the wooden barrel, an iron frame is 
placed, upon which the truss rests. Two barrels constitute a pier. 
The advantages claimed for the wooden caissons are that they can 
be put in without interfering with traffic, or without loss of time in 
sinking by the passage of trains. The objection to them is that they 
are not durable. 

605. Contents of Bridge Piers. The table on page 389 gives 
the quantity of masonry in bridge piers having rectangular cross 
sections and such dimensions on top and batters as occur most 
frequently (see §§ 584-87). The quantities in the first four columns 
cover most of the cases for highway and single track railway bridges; 
and the quantities in the last two columns are applicable to double 
track railway bridges. Since that portion of the pier below the 
water should have more or less pointed ends, and since there is 
likely to be an offset in the profile—particularly of high piers,— 
the quantities in the table (being for a rectangular cross section) are 
mainly useful in making preliminary estimates. 

The contents of piers of other dimensions than those in the table 
may be computed by the following formula : * 

contents = th l -f b (l -f- t) h 2 -f- 1-J- b 2 h 3 , 
in which l — the length on top under the coping, 

t — “ thickness on top under the coping, 
h — “ height to the under side of the coping, 
b = “ batter— i. e., b = or -fa. 

The length on the bottom = l + 2bh; and the thickness on the 
bottom = t -j- 2 b h. To illustrate the method of applying this for- 


* See foot-note, page 359. 







ART. 2 .] 


DETAILS OF CONSTRUCTION 


389 


TABLE 41. 

Contents of Bridge Piers having Rectangular Cross Section and 

the same Batter on all Faces. 


Height- 
top of 
Footing 

TO BOTTOM 
OF 

Doping. 


Dimension of the Pier on top under the Coping. 


5 ft. x 

20 ft. 

6 ft. x 

22 ft. 

6 ft. x 

34 ft. 

Batter 1 :12 

Batter 1 :24 

Batter 1 :12 

Batter 1 :24 

Batter 1:12 

Batter 1:24 

feet. 

cu. yds. 

cu. yds. 

cu. yds. 

cu. yds. 

cu. yds. 

cu. yds. 

5 

20.49 

19.49 

26.64 

25.53 

40.90 

39.33 

6 

25.07 

23.63 

32.51 

30.90 

49.84 

47.57 

7 

29.83 

27.85 

38.57 

36.36 

59.05 

55.93 

8 

34.74 

32.13 

44.81 

41.90 

68.52 

64.43 

9 

39.84 

36.52 

51.24 

47.55 

78.23 

73.04 

10 

45.09 

40.97 

57.86 

53.28 

88.23 

81.80 

11 

50.53 

45.51 

64.67 

59.09 

98.50 

90.68 

13 

56.14 

50.14 

71.69 

65.02 

109.02 

99.68 

13 

61.93 

54.85 

78.89 

71.02 

119.83 

108.83 

14 

67.91 

59.64 

86.31 

77.13 

130.90 

118.09 

15 

74.07 

64.52 

93.92 

83.33 

142.25 

127.49 

16 

80.40 

69.48 

101.72 

89.61 

153.88 

137.03 

17 

86.93 

74.53 

109.75 

96.00 

165.79 

146.69 

18 

93.65 

79.66 

117.98 

102.49 

177.99 

156.49 

19 

100.56 

84.87 

126.43 

109.06 

190.45 

166.40 

20 

107.66 

90.18 

135.07 

115.72 

203.22 

176.47 

21 

114.96 

95.57 

143.94 

122.49 

216.28 

186.67 

22 

122.46 

101.06 

153.01 

129.36 

229.60 

196.98 

23 

130.15 

106.62 

162.33 

136.34 

243.24 

207.45 

24 

138.04 

112.27 

171.84 

143.39 

257.17 

218.05 

25 

146.14 

118.03 

181.56 

150.53 

271.39 

228.79 

26 

154.45 

123.86 

191.53 

157.79 

285.91 

239.65 

27 

162.96 

129.79 

201.74 

165.17 

300.74 

250.67 

28 

171.69 

135.81 

212.16 

172.68 

315.87 

261.82 

29 

180.62 

141.93 

222.79 

180.18 

331.27 

273.09 

30 

189.77 

148.12 

233.68 

187.85 

347.01 

284.51 

32 

208.72 

160.81 

256.15 

203.47 

379.42 

307.78 

34 

228.54 

173.86 

279.58 

219.52 

413.06 

331.59 

36 

249.26 

187.30 

303.98 

235.98 

447.99 

355.99 

38 

270.91 

201.12 

329.36 

252.84 

484.17 

480.92 

40 

293.47 

215.32 

355.74 

270.13 

521.66 

406.43 

42 

316.98 

229.92 

383.17 

287.88 

560.51 

432.57 

44 

341.46 

244.91 

411.59 

306.02 

600.64 

459.22 

46 

366.90 

260.29 

441.05 

324.60 

642.15 

486.47 

48 

393.36 

276.09 

471.66 

343.66 

684.99 

514.33 

50 

420.82 

292.29 

503.32 

363.13 

729.24 

542.78 

52 

449.33 

308.90 

536.07 

383.08 

774.88 

571.80 

54 

478.86 

325.93 

569.96 

403.45 

821.98 

601.47 

56 

509.45 

343.38 

604.96 

424.29 

870.45 

631.71 

58 

541.13 

361.24 

641.11 

445.57 

920.41 

662.57 

60 

573.85 

379.52 

678.48 

467.42 

971.78 

694.02 







































390 


BRIDGE PIERS. 


[CHAP. XVI. 


mula, assume that it is required to find the contents of a pier 4 feet 
thick, 20 feet long on top, and 30 feet high, having a batter on 
all four faces of 1 inch per foot. Then l = 20, t — 4, b = y 1 ^, and 
the preceding formula becomes 

contents = 4 X 20 x 30 -f (20 -f 4) (30) 2 -f f X yfy X (30) 3 
=4,450 cubic feet. 

606. Cost. For a general discussion of the cost of masonry, see 
§§ 226-38 (pp. 153-60); and for data on the cost of bridge pier 
masonry, see § 235 (p. 157). 


i 




* 




CHAPTER XVII. 


CULVERTS. 

I 

Art. 1. Water Way Required. 

607. The determination of the amount of water way required in 
any given case is a problem that does not admit of an exact mathe¬ 
matical solution. Although the proportioning of culverts is in a 
measure indeterminate, it demands an intelligent treatment. If 
the culvert is too small, it is liable to cause a washout, entailing 
possibly loss of life, interruptions of traffic, and cost of repairs. 
On the other hand, if the culvert is made unnecessarily large, the 
cost of construction is needlessly increased. Any one can make a 
culvert large enough ; but it is the province of the engineer to 
design one of sufficient but not extravagant size. 

608. The Factors. The area of water way required depends 
upon (1) the rate of rain-fall, (2) the kind and condition of the 
soil, (3) the character and inclination of the surface, (4) the condi¬ 
tion and inclination of the bed of the stream, (5) the shape of the 
area to be drained and the position of the branches of the stream, 
(6) the form of the mouth and the inclination of the bed of the 
culvert, and (7) whether it is permissible to back the water up above 
the culvert, thereby causing it to discharge under a head. 

1. It is the maximum rate of rain-fall during the severest storms 
which is required in this connection. This certainly varies greatly 
in different sections ; but there are almost no data to show what it is 
for any particular locality, since records generally give the amount 
per day, and rarely per hour, while the duration of the storm 
is seldom recorded. Further, probably the longer the series of 
observations, the larger will be the maximum rate recorded, since 
the heavier the storm the less frequent its occurrence ; and hence a 
record for a short period, however complete, is of but little value 
in this connection. Further, the severest rain-falls are of compara¬ 
tively limited extent, and hence the smaller the area, the larger the 

391 



392 


CULVERTS. 


[CHAP. XVII. 


possible maximum precipitation. Finally, the effect of the rain-fall 
in melting snow would have to be considered in determining the 
maximum amount of water for a given area. 

2. The amount of water to be drained off will depend upon the 
permeability of the surface of the ground, which will vary greatly 
with the kind of soil, the degree of saturation, the condition of 
cultivation, the amount of vegetation, etc. 

3. The rapidity with which the water will reach the water 
courses depends upon whether the surface is rough or smooth, steep 
or flat, barren or covered with vegetation, etc. 

4. The rapidity with which the water will reach the culvert 
depends upon whether there is a well-defined and unobstructed 
channel, or whether the water finds its way in a broad thin sheet. 
If the water course is unobstructed and has a considerable inclina¬ 
tion, the water may arrive at the culvert nearly as rapidly as it 
falls; but if the channel is obstructed, the water may be much 
longer in passing the culvert than in falling. 

5. Of course, the water way depends upon the amount of area 
to be drained; but in many cases the shape of this area and the 
position of the branches of the stream are of more importance than 
the amount of the territory. For example, if the area is long and 
narrow, the water from the lower portion may pass through the 
culvert before that from the upper end arrives ; or, on the other 
hand, if the upper end of the area is steeper than the lower, the 
water from the former may arrive simultaneously with that from 
the latter. Again, if the lower part of the area is better supplied 
with branches than the upper portion, the water from the former 
will be carried past the culvert before the arrival of that from the 
latter ; or, on the other hand, if the upper portion is better supplied 
with branch water courses than the lower, the water from the 
whole area may arrive at the culvert at nearly the same time. In 
large areas the shape of the area and the position of the water 
courses are very important considerations. 

6. The efficiency of a culvert may be materially increased by so 
arranging the upper end that the water may enter it without being 
retarded (see § 639). The discharging capacity of a culvert can 
also be increased by increasing the inclination of its bed, provided 
the channel below will allow the water to flow away freely after 




ART. 1.] WATER WAY REQUIRED. 3tf'J 

having passed the culvert. The last, although very important, is 
frequently overlooked. 

7. The discharging capacity of a culvert can be greatly increased 
by allowing the water to dam up above it. A culvert will discharge 
twice as much under a head of 4 feet as under a head of 1 foot.. 
This can only safely be done with a well-constructed culvert. 

609. Formulas. The determination of the values of the differ¬ 
ent factors entering into the problem is almost wholly a matter of 
judgment. An estimate for any one of the above factors is liable 
to be in error from 100 to 200 per cent., or even more, and of 
course any result deduced from such data must be very uncertain. 
Fortunately, mathematical exactness is not required by the problem 
nor warranted by the data. The question is not one of 10 or 20 
per cent, of increase; for if a 2-foot pipe is insufficient, a 3-foot 
pipe will probably be the next size—an increase of 225 per cent.,— 
and if a 6-foot arch culvert is too small, an 8-foot will be used— 
an increase of 180 per cent. The real question is whether a*2-foot 
pq:>e or an 8-foot arch culvert is needed. 

Numerous empirical formulas have been proposed for this and 
similar problems ; * but at best they are all only approximate, since 
no formula can give accurate results with inaccurate data. The 
several formulas, when applied to the same problem, give very 
discordant results, owing (1) to the sources of error already re¬ 
ferred to and (2) to the formulas* having been deduced for localities 
differing widely in the essential characteristics upon which the 
results depend. For example, a formula deduced for a dry climate, 
as India, is wholly inapplicable to a humid and swampy region, as 
Florida ; and a formula deduced from an agricultural region is 
inapplicable in a city. 

However, an approximate formula, if simple and easily applied, 
may be valuable as a nucleus about which to group the results of 
personal experience. Such a formula is to be employed more as a 
guide to the judgment than as a working rule; and its form, and 
also the value of the constants in it, should be changed as subse¬ 
quent experience seems to indicate. With this use in view, a few 
formulas will be referred to briefly. 

There are two classes of these formulas, one of which purports 


* For a general note on empirical formulas, see § 364. 





394 


CULVERTS. 


[CHAP. XVII. 


to give the quantity of water to be discharged per unit of drainage 
area and the other the area of the water way in terms of the area of 
the territory to be drained. The former gives the amount of water 
supposed to reach the culvert; and the area, slope, form, etc., of 
the culvert must be adjusted to allow this amount of water to pass. 
There are no reliable data by which to determine the discharging 
capacity of a culvert of any given form, and hence the use of the 
formulas of the first class adds complication without securing any 
compensating reliability. Most of the formulas in common use for 
proportioning water ways belong to this class. Such formulas will 
not be considered here. 

The two following formulas belong to the second class. 

610. Myer’s Formula. Of the formulas giving a relation be¬ 
tween the area of water way and the area to be drained, Myer’s is 
the one most frequently used. It is 

^Area of water way, in square feet = G.\/ Drainage area, in acres, 

in which C is a variable co-efficient to be assigned. For slightly 
rolling prairie, C is usually taken at 1; for hilly ground at 1.5; and 
for mountainous and rocky ground at 4. For most localities, at 
least, this formula gives too large results for small drainage areas. 
For example, according to the formula, a culvert having a watei 
way of one square foot will carry the water from a single acre only. 
Further, if the preponderance of the testimony of the formulas for 
the quantity of water reaching the culvert from a given area can 
be relied upon, the area of water way increases more rapidly than 
the square root of the drainage area as required by this formula. 
Hence, it appears that neither the constants nor the form of this 
formula were correctly chosen; and, consequently, for small drainage 
areas it gives the area of waterway too great, and for large drain¬ 
age areas too small. 

611. Talbot’s Formula. Prof. A. N. Talbot proposed the fol¬ 
lowing formula, “more as a guide to the judgment than as a work¬ 
ing rule* 

Area of water way, in square feet = G {/(Drainage area, in acres) 3 , 

in which C is a variable co-efficient. Data from various States gave 
values for C as follows: “For steep and rocky ground, Ovaries 

* Selected Papers of the Civil Engineers’ Club of the University of Illinois, No. 2, 
pp. 14-17. 








ART. 1.] 


WATER WAY REQUIRED. 


395 


from § to 1. For rolling agricultural country subject to floods at 
times of melting of snow, and with the length of valley three or 
four times its width, 6 r is about and if the stream is longer in 
proportion to the area, decrease C. In districts not affected by 
accumulated snow, and where the length of the valley is several 
times the width, \ or -jf, or even less, may be used. C should be 
increased for steep side slopes, especially if the upper part of the 
valley has a much greater fall than the channel at the culvert.” 

The author has tested the above formula by numerous culverts 
and small bridges in a small city and also by culverts under high¬ 
ways in the country (all slightly rolling prairie), and finds that 
it agrees fairly well with the experience of fifteen to twenty years. 
In these tests, it was found that water ways proportioned by this 
formula will probably be slightly flooded, and consequently be com¬ 
pelled to discharge under a small head, once every four or five 
years. 

612. In both of the preceding formulas it will be noticed that 
the large range of the “ constant ” C affords ample opportunity for 
the exercise of good judgment, and makes the results obtained by 
the formulas almost wholly a matter of opinion. 

613. Practical Method. Valuable data on the proper size of 
any particular culvert may be obtained (1) by observing the existing 
openings on the same stream, (2) by measuring—preferably at time 
of high water—a cross section of the stream at some narrow place, 
and (3) by determining the height of high water as indicated by 
drift and the evidence of the inhabitants of the neighborhood. 
With these data and a careful consideration of the various matters 
referred to in § 608, it is possible to determine the proper area of 
water way with a reasonable degree of accuracy. 

Ordinarily it is wise to take into account a probable increase of 
flow as the country becomes better improved. However, in con¬ 
structing any structure, it is not wise to make it absolutely safe 
against every possible contingency that may arise, for the expen¬ 
diture necessitated by such a course would be a ruinous and un¬ 
justifiable extravagance. Washouts can not be prevented altogether, 
nor their liability reduced to a minimum, without an unreasonable 
expenditure. It has been said—and within reasonable limits it is 
true—that if some of a number of culverts are not carried away 




396 


CULVERTS. 


[CHAP. XVII. 


each year, they are not well designed; that is to say, it is only a 
question of time when a properly proportioned culvert will perish 
in some excessive flood. It is easy to make a culvert large enough 
to be safe under all circumstances, but the difference in cost be¬ 
tween such a structure and one that would be reasonably safe would 
probably much more than overbalance the losses from the washing 
out of an occasional culvert. It is seldom justifiable to provide for 
all that may possibly happen in the course of fifty or one hundred 
years. One dollar at 5 per cent, compound interest will amount to 
$11.47 in 50 years and to $131.50 in 100 years. Of course, the 
question is not purely one of finance, but also one of safety to human 
life; but even then it logically follows that, unless the engineer is 
prepared to spend $131.50 to avoid a given danger now, he is not 
justified in spending $1 to avoid a similar danger 100 years hence. 
This phase of the problem is very important, but is foreign to the 
subject of this volume. 

614. In the construction of a new railroad, considerations of 
first cost, time, and a lack of knowledge of the amount of future 
traffic as well as ignorance of the physical features of the country, 
usually require that temporary structures be first put in, to be re¬ 
placed by permanent ones later. In the mean time an incidental 
but very important duty of the engineer is to make a careful study 
of the requirement of the permanent structures which will ulti¬ 
mately replace the temporary ones. The high-water mark of streams 
and the effect of floods, even in water courses ordinarily dry, should 
be recorded. With these data the proper proportioning of the 
water way of the permanent structures becomes a comparatively easy 
task. Upon the judgment and ability displayed in this depends 
most of the economical value of the improvements; for, as the road 
will have fixed or standard plans for culverts, abutments, piers, 
etc., the supervision of the construction will not be difficult. 

Art. 2. Box and Pipe Culverts. 

615. Stone Box Culvert. This culvert consists of vertical side 
walls of masonry with flag stones on top from one Avail to the other. 
Masonry box culverts were constructed much more frequently for¬ 
merly than at the present time. The lack of suitable stone in many 
parts of the West led to the adoption of vitrified pipes (§ 627) and 
iron pipes (§ 631) instead of masonry box culverts. IioAvever, in 




ART. 2.] 


STONE BOX CULVERTS. 


39? 


many localities they are built frequently enough to warrant a brief 
discussion here. 

616. Foundation. A common foundation for masonry box cul¬ 
verts is a stone pavement (§ 219) under the entire culvert, upon 
which the side walls rest (see Fig. 91«). This is not good practice; 
for, since the paving is liable to be washed out, it endangers the 



wall. The tendency of the pavement to undermine may be dimin¬ 
ished (1) by driving sheet piling or by setting deep curb-stones at 
both ends, or (2) by extending the paving to a considerable distance 
beyond both ends. The first is the better method ; but usually 
these devices only postpone, and do not prevent, final failure. The 
water is nearly certain to carry the soil away from under the pave¬ 
ment, even if the curb-stones or sheet piles remain intact. 

Sometimes culvert foundations are paved by laying large stones- 
flatwise. This practice is no better than ordinary stone paving, un¬ 
less the flags are large enough to extend under both walls ; but 
stones large enough for this can seldom be obtained. 

A much better method is to give each side wall an independent 
foundation and to pave between the walls only (see Fig. 915). An 
important advantage of this method is that each wall can be placed 
separately, which facilitates the keeping of the water away from the 
foundation pit. Indeed, if the foundations are deep, or if there is- 
not much current, the paving may be entirely omitted. If the cur¬ 
rent is only moderate, it is sufficient to build in, at each end of the 
culvert, between the ends of the side walls with solid masonry up 
to the bed of the stream ; but if the culvert is long, it is wise to 
build one or more intermediate cross walls also. If the current is 
strong, the cross walls at the ends should be carried down deep, 
and the space between the side walls should be paved with large. 
stones closely set and deeply bedded. The best job possible is se¬ 
cured by setting the paving in cement mortar. In this connection* 
see Figs. 94, 95, and 96 (pages 403, 404, and 406). 

































398 


CULVERTS. 


[CHAP. XVII. 


The side walls and the cross walls (particularly at the end of the 
culvert) should have their foundations below the effect of frost. 

617. End Walls. The ends of box culverts are usually finished 
either with a plane wall perpendicular to the axis of the culvert as 
shown in Fig. 95 (page 404), or by stepping the ends off as shown 
in Fig. 92. Either form is liable to become clogged and to have 
its effectiveness greatly decreased, and probably its own existence 
endangered, by drift collected at its upper end. This danger is 





Fig. 92. 


Fig. 93. 


considerably decreased by extending the side walls at the upper end 
as shown in Fig. 93 and in Fig. 94 (page 403). If the mouth of 
the culvert should become stopped with drift, the open top is a well 
into which the water may fall. In this way the full discharging 
capacity of the culvert can be maintained. The lower end may be 
stepped as shown in Fig. 92. 

The wing walls may be made thinner at the outer end, thus pro¬ 
ducing to a small degree the same effect as is obtained in splaying 
the wings of arch culverts (see §§ G38-39). 

In this connection, see also Fig. 9G (page 406). 

618. Cover Stones. To deduce a relationship between the thick¬ 
ness of the cover stones and the load to be supported, let 

T = the thickness, in inches ; 

S = the span, in feet; 

H — the height of bank, in feet , above the top of the culvert; 

R -- the modulus of rupture, in pounds per square inch ; 

C — the co-efficient of transverse strength (§ 15) ; 

W = the total weight of the earth over the cover stone, in pourids . 










































ART. 2.] 


STONE BOX CULVERTS. 


399 


For simplicity, consider a section of the culvert only a foot long. 

The cover stones are in the condition of a beam supported at the 
ends and loaded uniformly. By the principles of the resistance of 
materials, one eighth of the uniform load multiplied by the span is 
equal to one sixth of the continued product of the modulus of rup¬ 
ture, the breadth, and the square of the thickness. Expressing 
this in symbols as above, and reducing, gives 


T = 



6 WS 
8 R " 



Ordinarily, earth weighs from 80 to 100 lbs. per cu. ft., but for 
convenience we will assume it at 100 lbs. per cu. ft., which is on 
the safe side ; then W = 100 H S. The maximum moving load for 
railroad bridges may be taken at, say, 2 tons per foot of track. 
This is distributed over at least 8 square feet; and hence the live 
load is equal to one quarter of a ton, or 500 pounds, per square foot, 
i. e. the live load is equal to an embankment 5 feet high. Therefore, 
the maximum live load—a locomotive—is provided for by adding 5 
feet to the actual height of the embankment. The table on page 
12 shows that for limestone R = 1,500. Substituting these values 
in equation (1), above, gives for limestone 

T=0.20 SVH+h, .(2) 

By substituting the corresponding value of R from the table on 

page 12, we have for sandstone 

T — 0.25 S (3) 

For highways , it is sufficiently exact to drop the 5 under the 

radical, i. e., to neglect the live load; and equation (1) then becomes 
for limestone 

T = 0.20 SVH, .(4) 

and for sandstone 

T=0.2hSVH. .(5) 

The preceding formulas give the thickness which a stone of 
average quality must have to be on the point of breaking; and hence 











400 


CULVERTS. 


[CHAP. XVIL 


in applying them it will be necessary to allow a margin for safety, 
either by selecting the stone or by increasing the computed thick¬ 
ness. If reasonable care is used in selecting the stones, it is probably 
safe to double the thickness found as above. To allow for any given 
factor of safety, multiply the thickness found by applying the above 
formulas by the square root of the factor of safety. Thus, to allow 
for a factor of 4, multiply the thickness found as above by 2 : for a 
factor of 6, multiply by 2} ; and for a factor of 9, multiply by 3. 

619. The thickness of the cover stones does not, however, de¬ 
pend alone upon the depth of the earth, the live load, and the span. 

In the first place, the pressure on the cover stone does not vary 
directly as the depth of the earth above it. («) The earth itself 
acts more or less as a beam to support part, at least, of the weight 
over the opening. That earth may act thus is proven by the fact 
that an excavation can be carried horizontally into an embankment 
nr side hill without supporting the roof. The beam strength of the 
earth increases with the compactness and the tenacity of the soil 
and with the square of the height of the embankment above the 
roof. This effect would be zero with clean sand ; but, owing to the 
nature of that material, it would seldom be employed for filling over 
a culvert. Hence, under ordinary conditions, part of the load is 
supported by the beam strength of the earth itself. Therefore, a 
low embankment may produce a greater strain in the cover than a 
much higher one. (#) The prism of earth directly over the culvert 
will be partially supported by the adjacent soil ; that is to say, the 
particles of earth directly above the culvert will act more or less as 
arches resting upon the earth at the sides of the culvert, thus par¬ 
tially relieving the cover stones. This effect would be greater with 
sharp sand than with clay, but would be entirely destroyed by shock, 
as of passing trains. ( c ) The stones at the center of the culvert 
would be relieved of part of their load by an action similar to that 
mentioned above, whereby the weight over the center of the culvert 
is transferred towards its ends. However, the relief caused by this 
' action is but slight. 

In the second place, the pressure due to the live load is trans- 
* mitted downward in diverging lines, thus distributing the weight 
over a considerably larger area than that assumed in deducing equa¬ 
tions (2) and (3) above. 

In the third place, the cover must be thick enough to resist the 




ART. 2 .] 


STOKE BOX CULVERTS. 


401 


effect of frost, as well as to support tlie earth and live load above it. 
The freezing, and consequent expansion, of the earth is a fo«ce 
tending directly to break the cover stones. That this is an impor¬ 
tant consideration is proved by the fact that these stones break 
near the ends of culverts as frequently as near the mid die, although 
the weight to be supported is greater at the latter place. 

620. It is impossible to compute, even approximately, the effect 
of the preceding factors ; but experience shows that the thickness 
is independent of the height of the embankment, provided there is 
sufficient earth over the cover stones to prevent serious shock,—say 
3 feet for railroads and 1 to 2 feet for highways. 

The thickness employed on the railroads in States along the 
fortieth parallel of latitude is generally about as follows, irrespec¬ 
tive of the height of the bank or of whether the cover is limestone 
or sandstone: 


Thickness of Cover. 
. 10 inches. 

. 12 inches. 

. 15 inches. 


Span of Culvert. 


2 feet, 

3 feet, 

4 feet, 


On the Canadian Pacific K. R., the minimum thickness of cover 
stones for spans of 3 feet is 16 inches, and under 3 feet, 14 inches. 

621. duality of Masonry. Box culverts are usually built of 
rubble masonry (§ 213) laid in cement mortar. Formerly they were 
often built of dry rubble, except for 3 or 4 feet at each end, which 
was laid in mortar. It is now generally held that box culverts 
should be so built that they may discharge under a head without 
damage. It is usually specified that the cover stones must have a 
solid, well-leveled bearing on the side walls of not less than 15 
inches. The most careful constructors close the joints between the 
cover stones by bedding spalls in mortar over them. 

622. Specifications .* All stone box culverts shall have a water way at least 
2| x 3 feet. The side walls shall not be less than two feet (2') thick, and 
shall be built of sound, durable stones not less than six inches (6") thick, laid 
in cement mortar [usually 1 part Rosendale cement to 2 parts sand], 4 be 
walls must be laid in true horizontal courses, but in case the thickness of the 
course is greater than 12 inches (12"), occasionally two stones may be used to 
make up the thickness. The walls must be laid so as to be thoroughly bonded, 
and at least one fourth of the area of each course must be headers going en- 


* Pennsylvania Railroad. 








402 


CULVERTS. 


[chap. xyil* 


tirel.y through the wall. The top course must have one half its area of through 
s^mes, and the remainder of this course must consist of stone going at least 
one half of the way across the wall from the inside face. The face stones of 
each course must be dressed to a straight edge, and pitched off to a true line. 
All of the coping stones of head walls must be throughs, and must have the 
upper surface hammer-dressed to a straight edge, and the face pitched off 
to a line with margin draft. Cover stones shall have a thickness of at least 
twelve inches (12") for opening of three feet (3'), and at least 14 inches (14") for 
opening of four feet (4'); and must be carefully selected, and must be of such 
length as to have a bearing of at least one foot (1') on either wall. 

The beds and vertical joints of the face stones for a distance of six 
inches (6") from the face of the wall shall be so dressed as to require a mortar 
joint not thicker than three fourths of an inch (£"). Joints between the cov¬ 
ering stones must be not wider than three fourths of an inch (£"), and the 
bearing surface of cover stones upon side walls must be so dressed as to 
require not more than a one-inch (1") mortar joint. 

The paving shall consist of flat stones, set on edge, at right angles with the 
line of the culvert, not less than twelve inches (12") deep, and shall be laid in 
cement mortar and grouted. 

623. Examples. The box culvert shown in Fig. 94 (page 403), 
is presented as being on the whole the best (see § 617). The table 
accompanying the diagram gives the various dimensions of, and also 
quantities of masonry in, box culverts for different openings. The 
former data and the diagrams are ample for the construction of any 
box culvert; while the latter data will be useful in making esti¬ 
mates of cost (§ 626). In the headings of the colums under “Size 
of the Openings,” the first number is the span of the culvert, and 
the second is the clear height of water way. The quantities of 
masonry in the table were computed for a cross wall at each end of 
the culverts, of the section shown in Fig. 94; but in many cases, 
this should be 3 feet deep instead of 2, as shown. In using the 
table this correction is easily applied. 

624. The box culvert shown in Fig. 95 is the one employed in 
the construction of the “West Shore R. R.”—New York City to 
Buffalo. The data in the table accompanying the diagram give the 
dimensions and quantities of masonry of various sizes. In the head¬ 
ings under “Size of the Openings,” the first number is the span of 
the opening and the second is its height. 

Box culverts of the general form shown in Fig. 95 are sometimes 
built double; i. e., two culverts are built side by side in such a 
manner as to have one side wall in common. The following table 




ART 


2 . 


] 


STONE BOX CULVERTS. 


403 


\ 



PH 

■M 

0 

◄ 

PS 

w 

ft 

w 

o 

p 

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0 

w 


50 


0 

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(-5 

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w 

0 

CE 

H 

ft 

g 

ft 

O 

o 

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<E 

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0 


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Ph 

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c* 

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10 

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C5 T-H 


CM 

TP 

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TP 


O O CO o o o* 


TP 

TP 


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Tp 


l'* rt 


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T—< 

05 00 0* cb o 


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be a 


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pf 

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as a 


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H_> . ZZ 


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PH 


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a - a 
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a 
a 



































































































404 




CULVERTS. 


[CHAP. XVII. 


Oi 


c 

HH 

55 

W 

0. 

o 

w 

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H 

6. 

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a 

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S <3 cs 


i 





















































































ART. 2.] 


STONE BOX CULVERTS. 


405 


gives the dimensions and quantities for such box culverts. The 
dimensions not given in the following table are the same as in the 
table accompanying Fig. 95. 

TABLE 44. 


Dimensions and Contents of Double Box Culverts. 




Size of the Opening. 


Items. 

2X2h 

feet. 

2h X 3 
feet. 

2j X 3J 
feet. 

3X4 

feet. 

4X5 

feet. 

Dimensions: 






End wall, length of. 

16' 6" 

20' 0" 

20' 0" 

23' 0" 

30' 0" 

Center wall, thickness of. 

2' o" 

2' 0" 

2' 0" 

2' 6" 

3' 0" 

Contents: 






Masonry in two end walls, in cu. yds. 

Masonry in trunk, per foot of length from in- 

13.16 

16.18 

21.50 

32.18 

53.25 

side to inside of end walls, in cu. yds. . . 
Paving in trunk, per foot of length from inside 

0.864 

0.982 

1.222 

1.778 

2.565 

to inside of end walls, in cu. yds. 

0.407 

0.444 

0.481 

0.592 

0.703 


The standard double box culvert employed in the construction 
of the Canadian Pacific R. R. differed from the form described 
above in having (1) shorter end walls, and wings at an angle of 30° 
with the axis of the culvert, and (2) a triangular cut-water at the 
upper end of the division wall. 

625. The culvert shown in Fig. 96 is the standard on the Inter¬ 
colonial Railway of Canada, and is very substantially constructed. 

626. Cost. With the data accompanying Figs. 94 and 95 (pages 
403 and 404), and the table of cost of masonry on page 160, it is 
an easy matter to make an estimate of the cost of a box culvert. 
For example, assume that it is proposed to build a culvert 30 feet 
long—out to out of culvert proper—having a water way 3 feet wide 
and 4 feet high, and that estimates of the cost of the general forms 
shown in Fig. 94 and also of that of Fig. 95 are desired. 

Estimates for a 3 X 4 ft. Box Culvert of the General Foi'm shown in Fig. 94. 

Masonry in 2 end walls—16.88 cu. yds.@ $3.50 per cu. yd. = $59.08 

“ “ 25 feet of trunk (1 444 x 25=) 36.10 cu. yds. @ $3.50 “ “ = 126.35 

Paving “25 “ “ “ (0.111x25=) 2.78 “ “ @ $2.00 “ “ = 5.55 

Total cost.$190.98 

Estimates far a 3 X 4 ft. Box Culvert of the General Form shown in Fig. 95. 

Masonry in 2 end walls—24.20 cu. yds.@ $3 50 per cu. yd. = $84.70 

“ “ 24 feet of trunk (24 x 1.148=) 27.55 cu. yds. @ $3.50 “ “ = 96.43 

Paving “ 24 “ “ “ (24 x 0.370=) 8.88 “ “ $2.00 “ “ = 17.76 

Total cost 


$198.89 



























S6ft 


406 


CULVERTS 


[CHAP. XVII. 






























































































































ART. 2.] 


vitrified pipe culverts. 


40 r 

If the price for the masonry does not include the expense for 
the necessary excavation, the above estimates should be increased 
by the cost of excavation, which will vary with the situation of the 
culvert. 

To make a comparison of the relative cost of the two types 
of culverts just mentioned, we may proceed as follows : The cost 
per foot of the trunk of a 3 X 4 culvert of the form shown in 
Fig. 94 is (1.444 cu. yds. of masonry @ $3.50 plus 0.111 cu. yds. 
of paving @ $2.00) $5.28; and the corresponding cost for Fig. 
95 is (1.148 cu. yds. of masonry @ $3.50 plus 0.370 cu. yds. 
of paving @ $2.00) $4.76. The difference in cost per foot 
is ($5.28 — $4.76) $0.52 in favor of Fig. 95. The cost of the 
end walls for Fig. 94 is (16.88 cu. yds. @ $3.50) $59.08; and the 
corresponding cost for Fig. 95 is (24.20 cu. yds. @ $3.50) $84.70. 
The difference is $25.62 in favor of Fig. 94. Since in the former 
the cross wall extends but 2 feet below the floor of the culvert, 
while in the latter the end walls extend 3 feet, the difference in cost 
should be decreased by the cost of the difference of the foundations. 
If the cross walls of Fig. 94 be carried down another foot, the 
amount of masonry will be increased 2 cu. yds. and the cost $7.00; 
and the difference in cost of the end walls will be ($25.62 — $7.00) 
$18.62 in favor of Fig. 94. Under these conditions, for a culvert 
40 feet long, the two types will cost the same; for lengths less than 
40 feet Fig. 94 is the cheaper, and for lengths greater than 40 feet 
Fig. 95 is the cheaper. If the end walls of Fig. 95 are carried 
down only 2 feet, the amount of masonry will he decreased by 3.4 
cu. yds. and the cost by $11.90; and then the difference of cost will 
be ($25.62 — $11.90) $13.72. Under this condition, for a culvert 
30 feet long, the two types will cost the same; for lengths less than 
30 feet Fig. 94 is the cheaper, and for lengths greater than 30 feet 
Fig. 95 is the cheaper. We may conclude, therefore, that for 
lengths under 35 or 40 feet the type shown in Fig. 94 is a little 
cheaper, while for greater lengths than 35 or 40 feet that in Fig. 
95 is slightly cheaper. For the smallest size the length of equal 
cost is about 10 feet. 

There is no material difference in the first cost of the two types; 
but the culvert shown in Fig. 94 is the more efficient. 

627. Vitrified Pipe Culverts. During the past lew years 
vitrified sewer pipes have been extensively employed for small cul- 




408 


• CULVERTS. 


[CHAP. XVII 


verts under both highways and railroads. The pipe generally 
employed for this purpose is that known to the trade as culvert 
pipe or “extra heavy” or “double strength” sewer pipe, which is 
20 to 40 per cent, (varying with the maker and the size) heavier than 
the quality ordinarily employed for sewers. 

Apparently the heavier pipe is used on the supposition that the 
lighter is not strong enough for culverts. In most cases, at least, 
this is an erroneous assumption. 1. With the same depth of earth 
over the pipe, there is but little more pressure on the pipe when 
used as a culvert than when employed in a sewer. At most, the 
difference of pressure is that due to the live load, which can not 
exceed the weight of an additional 5 feet of earth (see § 618), and 
will generally be much less (see the second paragraph of § 619). 
2. Experience demonstrates that the lighter pipes are not deficient 
in strength when used in sewers, however deep they are laid. 
Accordiug to experiments made by bedding the lower half of the 
pipe in sand and applying a pressure along a comparatively narrow 
area, the average crushing strength of ordinary sewer pipe w r as 
2,400 lbs. per sq. ft. of horizontal section, and for culvert pipe 
12,000 lbs. per sq. ft.* If the pressure had been applied more 
nearly as in actual practice, the pipes would have borne consider¬ 
ably more. The first of the above results is equal to the weight of 
24 feet of earth, and the second to that of 120 feet, although actual 
embankments of these heights would not give anything like the 
above pressures (see § 619). 

There is a little difference between culverts and sewers in the 
exposure to frost; but no danger need be apprehended from this 
cause, provided the culverts are so constructed that the water is 
carried away from the lower end, since ordinary soft drain tile are 
not in the least injured by the expansion of the frost in the earth 
around them. 

628. Construction. In laying the pipe, the bottom of the trench 
should be rounded out to fit the lower half of the body of the pipe, 
with proper depressions for the sockets. If the ground is soft or 
sandy, the earth should be rammed carefully, but solidly, in and 
around the lower part of the pipe. On railways, three feet of earth 
between the top of the pipe and the bottom of the tie has been 
found sufficient. On highways pipes have stood from 10 to 15 
years under heavy loads with only 8 to 12 inches of earth over 


* For additional data, see Note 7, page 547. 








ART. 2 .] 


VITRIFIED PIPE CULVERTS. 


409 


them; but as a rule it is not wise to lay them with less than 12 to 
18 inches of earth covering. 

In many cases—perhaps in most—the joints are not calked. If 
this is not done, there is liability of the water’s being forced out at 
the joints and washing away the soil from around the pipe. Even 
if the danger is not very imminent, the joints of the larger pipes, 
at least, should be calked with hydraulic cement, since the cost is 
very small compared with the insurance of safety thereby secured. 
Sometimes the joints are calked with clay. Every culvert should 
be built so that it can discharge water under a head without damage 
to itself. 

The end sections should be protected with a timber or masonry 
bulkhead, although it is often omitted. Of course a parapet wall 
of rubble masonry or brick-work laid in cement is best (see Fig. 97). 




The foundation of the bulkhead should be deep enough not to be 
disturbed by frost. In constructing the end wall, it is well to in¬ 
crease the fall near the outlet to allow for a possible settlement of 
the interior sections. When stone and brick abutments are too 
expensive, a fair substitute can be made by setting posts in the 
ground and spiking plank on as shown in Eig. 98. W hen planks 
are used, it is best to set them with considerable inclination towards 
the road bed to prevent their being crowded outward by the pressure 
of the embankment. The upper end of the culvert should be so 
protected that the water will not readily find its way along the out¬ 
side of the pipes, in case the mouth of the culvert should become 
submerged. 

The freezing of water in the pipe? particularly if more than 
half full, is liable to burst it; consequently the pipe should have a 
sufficient fall to drain itself, and the outlet should be so low that 



































410 


CULVERTS. 


[CHAP. XVII. 

there is no danger of back-water’s reaching the pipe. If properly 
drained, there is no danger from frost. 

When the capacity of one pipe is not sufficient, two or more 
may be laid side by side. Although two small pipes do not have 
as much discharging capacity as a single large one of equal cross 
section, yet there is an advantage in laying two small ones side by 
side, since then the water need not rise so high to utilize the full 
capacity of the two pipes as would be necessary to discharge itself 
through a single one of larger size. 

629, Examples. Fig. 99 (page 411) shows the standard vitri¬ 
fied pipe culverts employed on the Kansas City and Omaha R. R. 
This construction gives a strong, durable culvert which passes water 
freely. The dimensions of the masonry end walls and of the con¬ 
crete bed for the intermediate sizes are nearly proportional to those 
shown in Fig. 99. Table 46 (page 411) shows the quantities of 
masonry required for the principal sizes. 

630. Cost. Prices of vitrified pipe vary greatly with the con¬ 
ditions of trade, and with competition and freight. Current (1888), 
non-competitive prices for ordinary sewer pipe, in car-load lots 
f. o. 1). at the factory, are about as in the table below. 


TABLE 45. 

Cost and Weight of Vithified Sewer Pipe. 


Inside Diameter 

Price per Foot. 

Area. 

Weight per 
Foot. 

Amount in a 
Car Load. 

12 

inches. 

15 cents. 

.78 sq. 

ft. 

45 lbs. 

500 feet. 

14 

6 . 

23 

i ( 

1.07 “ 

( < 

55 “ 

400 “ 

16 

( 4 

30 

i < 

1.40 “ 

< < 

65 “ 

350 “ 

18 

< ( 

38 

« i 

1.76 “ 

c < 

75 “ 

300 “ 

20 

c i 

53 

a 

2.18 “ 

( i 

90 “ 

260 “ 

22 

(i 

57 

i c 

2.64 “ 

i i 

110 “ 

230 “ 

24 

( ( 

87 

a 

3.14 “ 

< < 

140 “ 

200 “ 


Culvert pipe costs about 20 to 25 per cent, more than as above, 
and second quality sewer pipe about 20 to 25 per cent. less. The 
latter differs from first quality in beiug less perfectly glazed, less 
perfectly burned, or not perfectly round, or in having fire cracks in 
the glazing, blisters on either surface, excrescences or pimples on 
the inside, or a piece broken out of the end. Frequently such 
pipe is as good for culverts as first quality sewer pipe. 



















ART. 2 .] 


VITRIFIED PIPE CULVERTS 


411 






Fig. 99.—Standard Vitrified Pipe Culvert.—K. C. & O. R. R. 


TABLE 46. 

Masonry Required for Vitrified Pipe Culverts of the General 

Form shown above. 


Items. 

Diameter of Pipe. 

14 inches. 

16 inches. 

20 inches. 

24 inches. 

Coping, two ends . 

Parapets, two ends . 

Total Masonry. 

cu. yds. 

0.54 

2.93 

cu. yds. 

0.71 

4.45 

cu. yds. 

0.97 

6.98 

cu. yds. 

1.07 

8.47 

3.47 

5.16 

7.95 

9.54 

Concrete, per lineal foot.. 

0.070 

0.102 

0.136 

0.180 




































































412 


CULVERTS. 


[CHAP. XVII. 


631. Iron Pipe Culverts. In recent years, iron pipes have 
been much used for culverts. In many localities good stone is not 
available, and hence stone box culverts (§§ 015-26) can not be used. 
In such localities vitrified stoneware pipes are used ; but as they 
are not made larger than 2 feet in diameter, iron or stone is the only 
material available for permanent culverts requiring a greater water 
way than that obtained by using one or two of the largest vitrified 
pipes. Apparently, stone culverts if well built should last forever; 
but, as constructed in the past, they have been found to last rela¬ 
tively only a short time. Hence, with the increasing cheapness of 
iron, there has been an increasing tendency to use iron pipe for even 
large culverts. Cast-iron pipes from 12 to 48 inches in diameter 
and 12 feet long are in common use by all of the prominent roads 
of the Mississippi Valley. Some of the roads cast their own, while 
others buy ordinary water pipe. The lightest water pipes made, or 
even such as have been rejected, are sufficiently strong. for use in 
culverts. The dimensions used on the Chicago, Milwaukee and St. 
Paul R. R. are about as follows: 

TABLE 47. 


Dimensions of Cast-Iron Culvert Pipe. 


Inside Diameter. 

Weight per Foot. 

Thickness. 

Weight per Lineal Foot 

PER SQ. FT. OF AREA. 

12 inches. 

60 lbs. 

T 7 ^ inch. 

77 lbs. 

16 “ 

88 “ 

4 “ 

63 “ 

20 “ 

118 “ 

1 “ 

59 “ 

24 “ 

175 “ 

1 “ 

56 “ 

30 " 

240 “ 

£ “ 

49 “ 

36 “ 

320 “ 

£ “ 

46 “ 

42 “ 

400 “ 

7 ‘ < 

"S' 

42 “ 

48 

510 “ 

1 " 

41 “ 


632. Construction. In constructing a culvert with cast iron, 
the points requiring particular attention are (1) tamping the soil 
tightly around the pipe to prevent the water from forming a chan¬ 
nel along the outside, and (2) protecting the ends by suitable head 
walls and, when necessary, laying riprap at the lower end. The 
amount of masonry required for the end walls depends upon the 
relative width of the embankment and the number of sections of 
pipe used. For example, if the embankment is, say, 40 feet wide 
at the base, the culvert may consist of three 12-foot lengths of 
















ART. 2.] 


IROK PIPE CULVERTS. 


413 

pipe and a light end wall near the toe of the bank; but if the 
embankment is, say, 32 feet wide, the culvert may consist of two 
12-foot lengths of pipe and a comparatively heavy end wall well 
back from the toe of the bank. The smaller sizes of pipe usually 
some in 12-foot lengths, but sometimes a few 6-foot lengths are 
included for use in adjusting the length of culvert to the width of 
hank. The larger sizes are generally 6 feet long. 

Fig. 100 (page 414) shows the method employed on the Atchi¬ 
son, Topeka and Santa Fe R. R. in putting in cast-iron jfipe 
culverts. Table 48 (page 414) gives the dimensions for the end 
walls for the various sizes. The length of pipe is determined by 
taking the multiple of 6 feet next larger than the length given by 
the position slope as in Fig. 100. To allow for settling, the pipe is 
laid to a vertical curve having a crown at the center of 1 inch for 
each 5 feet in vertical height from bottom of pipe to profile grade. 

Where the soil is treacherous, it would be wise to lay the pipes 
on a bed of broken stone to prevent undue settling. In this con¬ 
nection, see Figs. 96 and 99 (pages 406 and 411). 

633. Fig. 101 (page 415) shows the method employed on the 
Chicago, Burlington and Quincy R. R. of putting in cast-iron pipe 
culverts. This construction has given entire satisfaction. 

The same road has recently commenced the use of iron for cul¬ 
verts up to 12 feet in diameter. For diameters greater than 4 feet, 
the pipes are cast in quadrants 2, 4, 6, and 8 feet long, which are 
afterwards bolted together, through outside flanges, to form a 
cylinder of any desired length. The different segments are so com¬ 
bined as to break joints around and also along the pipe. The body 
of the pipe was formerly If inches thick ; but is now If, stiffened on 
the outside by ribs. The sections are put tpgether without any chip¬ 
ping, drilling, or other skilled labor. Between the different sec¬ 
tions is a recess in which a tarred rope smeared with neat cement 
mortar is placed before bolting the segments together, which makes 
tne joints tight.* 

634. Cost. The cost of cast-iron pipe varies greatly with com¬ 
petition and the conditions of trade. The price ranges from $26 to 
$36 per ton for first quality water pipes,/, o. b. at the foundry; or 
approximately, say, If cents per pound. 


* For illustration of details, see Railroad Gazette , vol. xix. pp. 123-24. 




414 


CULVERTS 


[CHAP. XVII 




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ART. 2 .] 


IRON PIPE CULVERTS. 


415 



Fi«. 101. -Cast-Iron Pipe Culvert.— C., B, & Q. R. R. 





































































































































































































































416 


CULVERTS. 


[CHAP. XVII. 


Table 47 (page 412) shows that the average weight of the pipe 
per foot per square foot of water way is about 60 pounds ; and 
hence the cost of the trunk of a cast-iron pipe, exclusive of trans¬ 
portation and labor, is about (60 X 1|) 90 cents per lineal foot per 
sq. ft. of area. The cost of sewer pipes is, from Table 46 (page 
411), about 22 cents per foot per square foot of water way ; and for 
culvert pipe about 30 cents. 

Assuming the cost of rubble masonry to be $3.50 per cubic yard 
and of paving to be $2.00 per cubic yard, the average cost of the 
masonry in the trunk of the box culvert shown in Fig. 95 (page 
404) is 40 cents per lineal foot for each square foot of water way ; 
and the corresponding cost for the culvert of Fig. 94 (page 403) is 
46 cents. The end walls required for these different forms of cul¬ 
verts are essentially the same ; and hence the above comparison 
' shows approximately the relative cost of the different forms of cul¬ 
verts. According to this showing, cast-iron pipe is the most ex¬ 
pensive ; but this difference is partly neutralized by the greater 
ease with which the iron pipe can be put into place either in new 
work or in replacing a wooden box-culvert. 

635. The following figures give the cost of a 7-foot cast-iron 
culvert of the form referred to in § 633, which see. 


42 ft. body $26.55 per foot (1.55 cents per pound). $1,114.83 

8 ft. specials @ $29.42 “ “ “ “ “ “ 235.32 

Bolts and washers. 29.91 

Unloading. 17.52 

Putting in place. 148.95 

"Stone for end walls, 70 cu. yds., @ $1.50. 105.00 

Stone for riprap foundation, 60 cu. yds., @ $1.00. 60.00 

Removing temporary bridge. 235.62 


Total. $1,947.15 


Excluding the cost of removing the temporary bridge—which 
is not a part of the culvert proper,—and of the riprap foundation— 
which the unusual conditions required,—the cost of the culvert was 
$33.03 per foot, or 83 cents per lineal foot for each square foot of 
water way. 

636. Timber Box Culverts. Timber box culverts should be 
used only where more substantial material is not attainable at a 
reasonable cost. Many culverts are constructed of timber an<J 














ART. 2 .] 


BOX AND PIPE CULVERTS. 


417 


periodically renewed with the same material, and many are con¬ 
structed of wood and replaced with stone, or sewer or iron pipe. 

The latter is an example of what may be called the standard 
practice in American railroad building; i. e., constructing the road 
as quickly and cheaply as possible, using temporary structures, and 
completing with permanent ones later as the finances of the company 
will allow and as the requirements of the situation become better 
understood. After the line is open, the permanent structures can 
be built in a more leisurely manner, at appropriate seasons, and 
thus insure the maximum durability at a minimum cost. 

There is a great variety of timber box culverts in common use, 
but probably there are none more durable and efficient than those 
used on the Chicago, Milwaukee and St. Paul R. R.,—shown in 
Pig. 102 (page 418).* On this road, it is the custom to replace the 
wooden boxes with iron pipes before the timber has seriously de¬ 
cayed. If experience has shown the size of the wooden box to be 
about right, the timbers are cut out a little and an iron pipe is 
placed inside of the box without disturbing the earth. 

For timber box culverts of sizes larger than can be made of 
plank, the Atchison, Topeka and Santa Fe R. R. employs bridge- 
tie box culverts. These are made by laying 6x8 inch sawed 
bridge ties flatwise, in contact, to form a floor. These ties are 
gained at the ends so as to leave a shoulder 1 inch deep against 
which the inside of the side walls bears. Upon this floor, vertical 
side walls are constructed by laying ties flatwise, one on top of the 
other; the lowest timber in each side wall is fastened to each tie in 
the floor by a drift-bolt 12 inches long, and each timber in the side 
wall is fastened to the one below it by a 12-inch drift-bolt every 3 
feet. The lengths of the ties employed in the side walls are so ad¬ 
justed as to make the exposed ends conform closely to the slope of 
the embankment. The roof consists of 6- X 8-inch ties set edgewise, 
in close contact, with a shoulder 1 inch deep on the inside, both 
ends of each piece being also drift-bolted to the side wall. 

637. Timber Barrel Culverts. For a number of years past 
the Chicago, Burlington and Quincy R. R. has found it desirable, 
in view of the absence or poor quality of the stone along its lines, to 
use a timber “barrel-culvert” when the opening is too large for a 


* From Railroad Gazette. 





418 


CULVERTS 


[chap. XVII, 



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ART. 3 .] 


ARCH CULVERTS. 


419 


timber box-culvert. The staves are 10 or 12 inches thick, accord¬ 
ing to the size of the culvert, and 8 inches wide on the outside, 
dressed to form a circle 4 \ or 6 feet in diameter. Iron rings—made 
of old rails—spaced about 10 feet apart, are used as a form upon 
which to construct the culvert and also to give it strength. The 
staves break joints and are drift-bolted (§ 381) together. As soon 
as the timber is thoroughly seasoned, the culverts are lined with a 
single ring of brick, and concrete or stone parapet walls are built. 
If, at any time, the timber fails, it is the intention to put iron pipe 
through the present opening. 

The timber costs about $12 per thousand feet, board measure, 
at the Mississippi River ; and the cost of dressing at the company^ 
shops is about $1.50 per thousand. 


Art. 3. Arch Culverts. 


638. In this article will be discussed what may be called the 
theory of the arch culvert in contradistinction to the theory of the 
arch. The latter will be considered in the next chapter. 

By the theory of the arch culvert is meant an exposition of the 
method of disposing a given quantity of masonry so as to secure (1) 
maximum discharging capacity, (2) minimum liability of being 
choked by drift, and (3) maximum strength. Attention to a few 
points, which are often neglected in the design of culverts, will se¬ 
cure these ends without additional cost. 

639. General Form of Culvert. Splay of Wings. There 

are three common ways of disposing the wing walls for finishing 
the ends of arch culverts. 1. The culvert is finished with a straight 
wall at right angles to the axis of the culvert (see Fig. 103). 2. The 



IMt 


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Fig. 105. 


wings are placed at an angle of 30° with the axis of the culvert 
(see Fig. 104). 3. The wing walls are built parallel to the 
axis of the culvert, the back of the wing and the abutment 
being in a straight line and the only splay being derived from thin- 




















4-20 


CULVERTS. 


[CHAP. XVII. 


ning the wings at their outer ends (see Fig. 105). The first method 
is shown on a larger scale in Plate II, the third in Plate III, and 
the second in Plate IV. 

The quantity of masonry required for these three forms of wings 
does not differ materially. Fig. 105 requiring the least and Fig. 103 
the most. The most economical angle for the wings of Fig. 104 is 
about 30° with the axis. 

The position of the wings shown in Fig. 104 is much the most 
common and is better than either of the others. Fig. 103 is ob¬ 
jectionable for hydraulic considerations which will be considered 
in the next section, and also because it is more liable to become 
choked than either of the others. Fig. 105 does not have splay 
enough to admit the natural width of the stream at high water, 
and does not give sufficient protection to the toe of the embankment. 

640. Junction of Wings and Body. With a culvert of the 

general form outlined in Fig. 104, 
there are two methods of joining 
the wings to the body of the cul¬ 
vert. The more common method 
is shown in Figs. 106 and 108; and 
the better, but less common, one is 
shown in Figs. 107 and 109. 

The form shown in Figs. 106 
and 108 is very objectionable because (1) the corners reduce the 
capacity of the culvert, and (2) add to its cost. 




1. The sharp angles of Fig. 106 materially decrease the amount 
of Vater which can enter under a given head and also the amount 





























































































ART. 3.] 


ARCH CULVERTS. 


42l 


'which can be discharged. It is a well-established fact in hydraulics 
that the discharging capacity of a pipe can be increased 200, or 
■even 300, per cent, simply by giving the inlet and outlet forms some¬ 
what similar to Fig. 107. Although nothing fixe this increase can 
be obtained with a culvert, one finished at both the upper and the 
lower end like Fig. 107 will discharge considerably more water than 
one like Fig. 106. The capacity of Fig. 107 decreases as the angle 
between the wing and the axis increases ; hence, the less splay the 
better, provided the outer ends of the wings are far enough apart 
to accommodate the natural width of the stream at high water. 
Also the less the splay, the less the probability of the culvert's being 
choked with drift. Fig. 106 is very bad for both the admission and 
the discharge of water, and also on account of the great liability 
that drift and rolling stones will catch in the angles between the 
wings and the end walls. In this latter respect Fig. 108 is slightly 
better than Fig. 106. 

2. Every angle adds materially to the cost of the masonry. In 
a culvert like Fig. 106, there are four unnecessary corners. This 
form probably owes its prevalence to the desire to have a uniform 
batter on the face of the wing, and to have the face of the wing 
wall intersect the end wall back of the arch stones. Satisfying both 
of these conditions gives a culvert in ground plan like Fig. 106 ; 
and satisfying the second one only, gives Fig. 108. Practically 
there is but little difference between these two forms—both are 
objectionable, as already explained. If the wing of Fig. 108 is 
moved inward, and the corner of the wing, which would other¬ 
wise project into the water way, is rounded off to a gentle curve, * 
Fig. 109 is obtained. This form is simple, efficient, and, on the 
whole, the best. 

Plate III shows another method of joining the wing to the 
-end wall without having an unnecessary angle. In this case, the 
face of the wing up to the springing line of the arch is a warped 
surface, which is in some respects undesirable, although it saves 
a little masonry. However, the face of the wing wall could be 
built vertical up to the springing line and then battered; or 
the wing could be moved forward and the corner be rounded off 
•as in Fig. 109. 

641. Semi-circular vs. Segmental Arches. There are two 
classes of arches employed for culverts, viz., the semi-circular and 



422 


CULVERTS. 


[CHAP. XVII. 


the segmental. The first is by far the more common; but neverthe¬ 
less the latter is, on the whole, much the better. 

1. For the same span, the segmental arch requires a shorter in~ 
trados (the inside curve of a section of the arch perpendicular to 
its axis). For example, the culverts shown in Plates IV and V 
have the same span, but the intrados of the semi-circular arch is 
15.71 ft., while that of the segmental arch is 10.72 ft.; that is, the 
intrados of the segmental is only 68 per cent, of the intrados of the 
semi-circular arch. This difference depends upon the degree of 
flatness of the segmental arch. The above example is an extreme 
case, since the segmental arch is unusually fiat, the central angle 
being only 73° 44'. (The rise is one sixth of the span.) With a 
central angle of 120°, the intrados of the segment is 77 per cent, of 
the semi-circle. 

Or, to state the above comparison in another and better form, for 
the same length of intrados the segmental arch gives the greater 
span. For example, a segmental arch on the same general plan as 
that of Plate V, but having an intrados equal to that of Plate IV, 
would have a span of 14.64 ft., which is 46 per cent, greater than 
the span of the semi-circular arch shown in Plate IV. A segmental 
arch with a central angle of 120° has a span 33 per cent, greater 
than a semi-circular arch having the same length of intrados. This 
difference constitutes an important advantage in favor of the seg¬ 
mental arch culvert, since the wider the span the less the danger of 
the culvert's being choked by obstructions, and because it will pass 
considerably more water for the same depth. 

2. For the same length of intrados, the segmental arch gives the- 
greater water way. The water way of the culvert shown in Plato 
IV is 87.6 square feet; but the same length of intrados in a seg¬ 
mental arch culvert having 73° 44' central angle (the same as Plate 
V) would have a water way of 98.3 square feet; and with a central 
angle of 120° would have a water way of 99.5 square feet. In both 
examples the increase is one eighth. 

3. On the other hand, the segmental culvert will require a 
thicker arch. It will be shown in the next chapter that arches 
can not be proportioned strictly in accordance with mathematical 
formulas ; and hence the exact difference in thickness of arch which 
should exist between a semi-circular and a segmental arch can not 
be computed. According to established rules of practice, small 




ART. 3.] 


ARCH CULVERTS. 


423 


segmental arches are from 10 to 25 per cent, thicker than semi¬ 
circular ones. This dilference is not very great, and its effect upon 
the cost of the culvert is, proportionally, still less, since the cost 
per yard of arch masonry is less for the thicker arches. Then, we 
may conclude that, since for the same span the intrados of seg¬ 
mental arches is from 20 to 40 per cent, shorter than the semi¬ 
circle, the segmental arch requires a less volume of arch masonry 
than the semi-circular, and also costs less per cubic yard. The arch 
masonry per foot of length of the segmental arch culvert shown in 
Plate V is only 71 per cent, of that in the semi-circular one shown 
in Plate IV. The dimensions and contents of arch culverts of the 
general forms shown in Plates IV and V are given in Tables 51 
and 52 (pp. 430 and 431 respectively), from which it appears that 
the segmental arch contains only from 60 to 76 per cent, as much 
masonry as the semi-circular, the average for the six spans being 
almost exactly 70 per cent. The cost of these two classes is shown 
in Tables 56 and 57 (pages 437 and 438), from which it appears that 
the average cost of segmental culverts 20 feet long and of different 
spans is only 59 per cent, of the cost of semi-circular ones of the 
same length and span; and the average cost of an additional foot 
in length for the segmental is only 86 per cent, of that for a circular 
one. The water ways of the semi-circular culverts are a little the 
greater, and hence the difference in cost per square foot of water 
way is not as great as above; but, on the other hand, the form of 
water way of the segmental culvert is the more efficient, and hence 
the above comparison is about correct. 

4. Will the segmental, i. e., the flatter, arch require heavier abut¬ 
ments (side walls)? Unquestionably the flatter the arch the 
greater the thrust upon the abutment; but the abutment not only 
resists the thrust of the arch which tends to turn it over outwards, 
but also the thrust of the embankment, which tends to push it in¬ 
wards. It is impossible to compute, with any degree of accuracy, 
either the thrust of the arch or of the embankment; and hence it is 
impossible to determine either the relative value of these forces or the 
thickness which the two abutments should have. Experience seems 
to indicate that the thrust of the earth is greater than that of the 
arch, as is shown by the fact that nearly all semi-circular culverts 
have abutments of much greater thickness than are required to re¬ 
sist the thrust of the arch; and hence we may conclude that expe- 



424 


CULVERTS. 


[CHAP. XVII. 


rience has shown that the thrust of the earth necessitates a heavier 
abutment than does the thrust of the arch. If this be true, then 
the abutment for segmental arches may be thinner than those for 
semi-circular ones; for, since the thrust of the former is greater 
than the latter, it exerts a greater force outward, which counter¬ 
balances a larger part of the inward thrust of the embankment, and 
thus leaves a less proportion of the latter to be resisted by the mass 
of the abutment. Segmental arch culverts are not often built; and 
designers appear to have overlooked the thrust of the earth, since 
the side walls of segmental arches are generally thicker than for 
semi-circular ones (compare Plates IV and V). 

The conclusions may, therefore, be drawn that segmental arch 
culverts are both cheaper and more efficient than semi-circular ones. 

642. As built, many semi-circular arches are practically seg¬ 
mental; that is, the side walls are built so high, or the backing is 
made so heavy, that practically the abutments are less than 120° 
apart, and hence the two lower ends of the arch are really only a 
part of the side wall, and should be built square. 

Further, it is shown in §§ 681-82 that a true arch of more than 
about 90 to 120 degrees is impossible. 

643. Examples. Under this head will be given a brief descrip¬ 
tion of four series of arch culverts which are believed to be repre¬ 
sentative of the best practice. 

644. Illinois Central Arch Culverts. Plate II shows the gen¬ 
eral plan of the standard arch culvert employed in the construction 
(1852-53) of the Chicago branch of the Illinois Central Railroad.* 
While the timber in the foundation is apparently still in good con¬ 
dition, the use of timber for such shallow foundations can not be 
considered as the best construction. However, many of the con¬ 
ditions, particularly drainage, have greatly changed since this road 
was built, and it is by no means certain that this use of timber 
was not good practice at that time (see § 636). 

Table 49 (page 425) gives the dimensions and contents for the 
several spans of this form of culvert. The contents of the end 
walls were computed on the assumption that the off-set at the back 
was 6 inches for each foot, counting from the top, until the full 
thickness at the bottom was obtained (see Section E-F, Plate II). 


* Published by permission of J. M. Healey, Division Engineer. 





TABLE 49.— Dimensions and Contents of Illinois Central Arch Culverts. 

FOR DIAGRAM SEE PLATE II. 

Dimensions not given in the table are the same, for all sizes, as in the diagram. 


ART. 3.] 


ARCn CULVERTS 


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426 


CULVERTS. 


[CHAP. XVII. 


645. Example of the Use of Table 49. To illustrate the method 
of using the above table, assume that an estimate of the amount of 
material in an 8-ft. arch culvert of the preceding form is required. 
Assume that the top of the coping is 3 feet below sub-grade, i. e ., 
that there is 4.25 feet of earth above the crown of the arch. Assume 
also that the road bed is 16 feet, and that the slope of the embank¬ 
ment is H to 1. Then the length of the culvert from inside to in¬ 
side of the end walls will be 16 -j- 2 (f X 3) = 16 -f- 9 = 25 feet; and 
from out to out of end walls, the length will be 25 -f 2 X 2.5 = 30 
feet. 

Assuming that the timbers under the planking are 8x10 inches, 
the 205 sq. ft., as per the table, will require 1,422 ft. B. M. of tim¬ 
ber, or 9 pieces 24 ft. long. Notice, however, that in practice 10 
pieces would be used—5 at each end of the culvert. The length of 
the trunk of the foundation is 30 — 2 (4-J- 4 -f-1) = 19 ft. Hence 
the area under the trunk of the foundation to be covered with tim¬ 
ber is 19 X 8 (see table) = 152 sq. ft.; and if 8 X 10-inch timbers 
are used, this will require 1,216 ft. B. M., or 12 pieces 14 feet long. 
The plank under the wings and in the sheet piling is 1,493 feet (see 
table), and that in the trunk is 32 (see table) X19 = 608 ft. B. M.; 
hence the total plank is 1,493 -f- 608 = 2,101 ft. B. M. 

The masonry in the end wall is 32.97 cu. yds., as in table. The 
masonry in 1 foot of arch is (see table) 0.673 -f- 0.284 = 0.957; and 
in 30 ft. it is 0.957x30 = 28.71 cu. yds. The masonry in the side 
walls (abutments of the arch) is 0.444 (see table) X30 = 13.32 cu. 
yds. The coping is 65 cu. ft. (see table) = 2.41 cu. yds. 

Collecting and tabulating the preceding results, we have the 
following: 


Timber:—10 pieces, 8 X 10 inches, 24 ft. long. 1,600 ft. B. M. v 

12 “ “ “ 14 “ “. 1,120 “ “ 

2-inch plank. 2,101 “ “ 


Total timber in culvert 25 ft. long_ 4,821 “ ** 

Masonry:—2 end walls. 33.0 cu. yds. 

coping. 2.4 “ “ 

side walls (abutments). 13.3 “ “ 

arch masonry. 28.7 “ “ 


Total masonry in culvert 25 ft. long.. 77.4 “ “ 











ART. 3.] 


ARCH CULVERTS. 


AO 7 

-A-'V | 


646. Chicago, Kansas and Nebraska Arch Culverts.—The culvert 
shown in Plate III is the standard form employed on the Chicago, 
Kansas and Nebraska Railroad.* Notice that the slope line inter¬ 
sects the inside face of the end wall at a considerable distance above 
the back of the crown of the arch (see Side View, Plate III). This 
is sometimes urged as an objection to this form of construction, on 
account of the supposed liability of the top of the end wall being 
pushed outward; but there is no danger of this method of failure, 
since the height of the end wall above the crown of the arch is, ex¬ 
clusive of the coping, only equal to its thickness, and in addition it 
is buttressed on the outside by the wings. The advantage of this 
construction is that it requires less masonry and also less labor. 

Concerning the manner of joining the wings to the body, see the 
last paragraph of § 640 (page 421). 

Table 50 (page 428) gives the dimensions and contents for 
various spans. The contents of the wings above the springing line 
of the arch were computed for courses 1 foot thick and for an earth 
slope of 1 i to 1 (see §557). 

647. Example of the Use of Table 50. Assume the same depth 
of earth over the crown of the arch as in the example in §644, 
i. e., 4.25 ft.; and assume also that the slope line strikes the upper 
corner of the coping instead of the lower as shown in Plate III. 
The top of the coping will be 0.75 ft. below sub-grade; and, for a 
16-ft. road-bed, the length of the arch—inside to inside of end 
walls—is 16 -f- 2(f X 0.75) = 18.25 ft. With the above data and 
Table 50, we have the following: 


Four wing walls, including one footing course, . . 40.5 cu. yds. 

Two head “ “ “ “ “ . . 36.8 “ “ 

Coping,. 1.8 “ “ 

Two side walls, 184 ft- @ 1.382 cu. yds. per foot, . . 25.2 “ “ 
Arch masonry, “ “ “1.184“ “ “ “ . . 21.6“ “ 
Paving, 23.58 ft. 0.272 cu. yd. per ft., . . . 6.4 “ “ 


Total masonry in culvert 184 ft- long, . . 132.3 “ <s 


In attempting to make comparisons between the above total and 
that of § 645, notice that the culverts are of very different style (see 
§§ 638 and 639) and that the water ways are of different areas. 


* Published by permission of H. A. Parker, Chief Engineer. 








TABLE 50. 

Dimensions and Contents of Chicago, Kansas and Nebraska Arch Culverts. 


CULVERTS 


[CHAP. XVIL 


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ART. 3.] 


ARCH CULVERTS. 


429 


648. Atchison, Topeka and Santa F6 Arch Culverts. Plates 
IV and V show the standard semi-circular and segmental arch cul¬ 
verts used by the Atchison, Topeka and Santa Fe Kailroad.* 

Tables 51 and 52 give the dimensions and contents for the 
several spans. Notice that the heights of the end walls do not vary 
uniformly, that for the 12-foot span being proportionately too great; 
and consequently the contents of the end walls and of the wings do 
not vary uniformly. The contents of the facing of the wings were 
computed for courses 18 inches thick (see § 557), and the backing 
was computed on the assumption that the back surface was a plane 
such that the dimension at the outer end and also where a plane 
parallel to the section E-F passes through the corner of the end 
wall is as in the diagram. 

In computing the masonry in a given culvert, these tables are to 
be employed as already explained for Tables 49 and 50—see §§ 645 
and 647. 

649. Standard Arch Culvert. The culvert shown in Plate VI 
has been designed in accordance with the principles laid down 
in the preceding discussion (§§ 638-41). The wings are joined to 
the body in such a manner as to offer the least possible resistance 
to the passage of water and drift. If the current is slow and not 
liable to scour, the paving may be omitted, since the end walls, being 
continuous under the ends of the water way, will prevent under¬ 
mining of the side walls; or, in long culverts, one or more inter¬ 
mediate cross walls may be constructed. But ordinarily the money 
paid for paving is a good investment. If the current is very rapid, 
it is wise to grout the paving,—and also to inspect the structure 
frequently. 

The arch ring is amply strong to support any bank of earth (see 
Table 63, page 502, particularly Nos. 9, 12, 18, 53, 54, and 61). 
The strains in a masonry arch can not be computed exactly; but the 
best method of analysis (§ 688) shows that if the earth is 10 feet 
thick over the crown, the maximum pressure is not more than 55 
pounds per square inch (compare with § 222 and also t §§ 246—48). 
A greater thickness of earth at the crown would doubtless increase 
the maximum pressure in the arch; but proportionally the pressure 
would increase much less rapidly than the height of the bank (see 


* Published by permission of A. A. Robinson, Chief Engineer. 






Dimensions and Contents op Atchison, Topeka and Santa Fe Semi-Circular Arch Culverts. 


430 


CULVERTS 


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TABLE 52. 

Dimensions and Contents of Atchison, Topeka and Santa Fe Segmental Arch Culverts. 

FOR DIAGRAM SEE PLATE V. 

Dimensions not given in the table are the same, for all sizes, as in the diagram. 


ART. 3.] 


ARCH CULVERTS 


431 


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432 


CULVERTS. 


[CHAP. XVII. 


§ G19). The arch is also stable under any position of the moving 
load, with either a heavy or a light embankment. The joints of 
the abutment are radial, to prevent any possibility of failure by 
the sliding of one course on another (see § 674). 

Table 53 (page 433) gives the dimensions and contents of various 
sizes. In each case the rise is one fifth of the span, the central 
angle is 87° 12', and the height of the opening is equal to half the 
span. The paving and coping were each assumed to be 1 foot thick; 
but for any other thickness it is only necessary to increase or de¬ 
crease the tabular numbers proportionally. The contents of the 
wings were computed on the assumption that all the courses were 1 
foot thick (see § 557). 

650. Quality of Masonry. The masonry of arch culverts is 
usually divided into two classes; the first consists of the masonry in 
the wings and end walls (parapet), and the second of the arch 
stones. The former is classified as first-class or second-class ma¬ 
sonry (see § 225). Only the masonry in the arch stones is called 
arch masonry. The arch stones which show at the end of the arch 
are called ring stones, and the remainder of the arch stones the 
arch sheeting. The arch masonry proper is usually classified as 
first-class or second-class arch masonry. The distinction between 
these two classes is usually about as in the specifications below. 

651. Specifications.* Foundations. “When the bottom of the pit is 
common earth, gravel, etc., the foundations of arch culverts will generally 
consist of a pavement formed of stone, not less than twelve inches (12") in 
depth, set edgewise, and secured at the ends by deep curbstones which must 
be protected from undermining by broken stone placed in such quantity and 
position as the engineer may direct. When the bottom upon which a culvert 
is to be built is soft and compressible, and where it will at all times be 
covered with water, timber well hewn, and from eight (8) to twelve inches 
(12") in thickness, according to the span of the culvert, shall be laid side by 
side crosswise upon longitudinal sills; and when the position of the culvert is 
such that a strong current will be forced through during floods, three courses 
of sheet piling shall be placed across the foundation—one course at each end, 
and one in the middle,—which shall be sunk from three (3) to six feet (6') 
below the top of the timber, according as the earth is more or less compact.”! 

652. First-Class Arch Masonry. “ First-class arch masonry shall be built 
in accordance with the specifications for first-class masonry [§ 225], with the 
exception of the arch sheeting and the ring stones. The ring stones shall be 


* See also Specifications for Railroad Masonry, Appendix 1. 
t Pennsylvania Railroad. 




Dimensions and Contents of Standard Arch Culverts. 


AKT. 3.] 


AKCJI CULVEKTS 


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434 


CULVERTS. 


[CHAP. XVII. 


dressed to such shape as the engineer shall direct. The ring stones and the 
arch sheeting shall he of stone not less than ten inches (10") thick on the 
intrados, shall be dressed with three eighths of an inch (f") joints, and shall 
be of the full depth specified for the thickness of the arch; and the joints 
shall be at right angles to the surface of the intrados. The face of sheeting 
stones shall be dressed to make a close centering joint. The ring stones and 
the sheeting shall break joints not less than one foot O'). 

“ The wings shall be neatly stepped with selected stones of the full width 
of the wing and of not less than ten inches (10") in thickness, which shall 
overlap by not less than eighteen inches (18"); or shall be finished with a 
neatly-capped newel at the free end, and a coping course on the wing. The 
parapets shall be finished with a coping course not less than ten inches (10") 
thick and of the full width of the parapet, which shall project six inches (6"). 

653. Second-Class Arch Masonry. “Second-class arch masonry is the 
same as second-class masonry [§ 225], with the exception of the arch sheeting. 
The stones of the arch sheeting shall have a good bearing throughout, and 
shall be well bonded and of the full depth of the thickness of the arch. No 
stone shall be less than four inches (4") in thickness on the intrados. Ring 
stones of all arches over eight feet (8') span shall be dressed according to 
specifications for first-class arch masonry [§ 651]." * 

654. Paving. For specifications for Paving, see § 219 (page 148), and 
also Specifications for Railroad Masonry, Appendix I. 

655. Cost. §§ 226-38 contain data on the cost of masonry, of 
which the last is a summary. Table 17 (page 159) contains a de¬ 
tailed statement of the actual cost of the masonry in an arch 
culvert; and below are the items of the total cost of that culvert. 


613 cu. yds. of masonry @ $6.59, $4,036.85 

Excavations—foundations and drainage,. 263.36 

Sheet piling,. 19.69 

Concrete,. 43.75 

Extra allowance on sheeting stones,. 20.00 


Total cost of culvert,.$4,383.65 


The total cost of the culvert per yard of masonry is $7.16,—which 
is uuusually low. 

Below is the total actual cost of the 8-ft. culvert (length out to 
out of end walls = 30 ft.) for which the quantities were estimated 
in § 645 (page 426). 


* Atchison, Topeka and Santa F6 R. R. 











ART. 3 .] 


ARCH CULVERTS. 


435 


Wall masonry—48.7 cu. yds. @ $7.00,.$340.90 

Arch masonry—28.7 “ “ “ 8.50,. 243.95 

Timber—5,247 ft., B M., @ $40.00,. 209.88 

Excavating foundations and straightening stream 158 cu. 

yds. 50c.,. 79.00 


Total cost of culvert.$873.73 


The total cost of this culvert per cubic yard of masonry is $11.29. 
The average total cost of a number of representative culverts of 
this style was $11.46 per cubic yard of masonry, being practically 
constant for all spans. 

656. Illinois Central Culverts. Table 54 gives the cost of cul¬ 
verts 25 feet long—out to out of end walls—of various spans of the 
general plan shown in Plate II, and will be very useful in estimat¬ 
ing the cost of such culverts. The quantities of masonry necessary 
to compute Table 54 were taken from Table 49 (page 425). The 
prices are believed to be fair averages (see page 160) for the first- 
class masonry described in § 651. The prices are the same as 
actually paid by the Illinois Central Railroad, except for arch 
masonry and excavation, for which $8.50 and 50c. respectively were 
paid. The prices used in deducing the table are given therein, and 
hence the results can be modified for prices differing from those 
there employed by simply taking proportional parts of the tabulated 

TABLE 54. 

Cost op Illinois Central Arch Culverts 25 Ft. Long from Out to 
Out of End Walls, and also of each Additional Foot. 

FOR DESCRIPTION SEE PAGE 424. 


Items. 

Span. 

4 

6 ft. 

8 ft. 

10 ft. 

12 ft. 

Plain masonry $7.00 per cu. yd. 

Arch masonry 8.00 “ “ “ . 

Timber and plank at $40 per M. ft., B. M. 

Excavating foundation 25c. per cu. yd. 

Total cost of culvert 25 ft. long. 

Cost of an Additional Foot of Length: 

Plain masonry $7.00 per cu. yd. 

Arch masonry 8.00 “ “ “. 

Timber and plank @ $40 per M ft., B. M. 

Excavation 25c. per cu. yd. 

Total cost of 1 additional foot. 

$237.35 

151.29 

150.88 

12.48 

$325.29 

191.29 

188.12 

15.85 

$424.97 

255.29 

232.84 

19.22 

$455.98 

362.82 

268.92 

21.38 

$552.00 

$3.11 

6.05 

3.36 

.32 

$720.55 

$3.11 

7.65 

3.84 

.40 

$932.32 

$3 11 
10.21 
5.04 
.48 

$1,109.10 

$3 63 
14.51 
5.88 
.56 

$12.84 

$15.00 

$18.84 

$24.48 









































436 


CULVERTS. 


[CHAP. XVII. 


quantities. The amount of excavation used in computing the table 
is the mean of the actual quantities for a number of representative 
culverts as constructed on the above road. 

657. Chicago, Kansas and Nebraska Culverts. Table 55 is given 
to facilitate estimating the cost of culverts of the general form 
shown in Plate III. The prices are about the average for the 
respective kinds of work; but in case it is desired to determine the 
cost for other prices, it is only necessary to increase or decrease the 
tabular numbers proportionally. The quantities of excavation are, 
approximately, averages of the actual amounts for a number of 
similar culverts, and are equivalent to a pit 2 feet 2 inches deep and 
of an area equal to the area of the foundation. The table includes 
only one footing course, but in so doing it is not intended to imply 
that one is always, or even generally, enough. Notice that the cul¬ 
vert in Table 55 is 25} feet long from outside to outside of end 
walls, and hence is one third of a foot longer than that presented in 
Table 54. 

658. A., T. and S. F, Semi-circular Culverts. Table 56 is similar 
to the two preceding ones, and shows the cost of the Atchison, 

TABLE 55. 

Cost of C K. and N. Arch Culverts 20 Ft. Long from Inside to 
Inside of Coping, and also of each Additional Foot of Length. 

FOR DESCRIPTION SEE PAGE 427. 

This table includes one footing course. 


Items. 



Span. 



3 ft. 

4 ft. 

6 ft. 

8 ft. 

10 ft. 

Plain masonry @ $7.00 per cu. yd. 

$217.98 

$397.04 

$657.23 

$703.43 

$853.16 

Arch masonry @ 8.00 “ “ “. 

44.64 

79.03 

130.78 

239.92 

346 96 

Paving 2.00 “ “ “. 

4.42 

6.32 

10.16 

13.96 

17 76 

Excavation @ .25 “ “ “. 

7.44 

9.33 

12.42 

13.95 

14.99 

Total cost of culvert 20 ft. long ... 

$274.48 

$491.72 

$810.59 

$971.26 

$1,232.87 

Cost of an Additional Foot of 
Length: 

Plain masonry @ $7.00 per cu. yd. 

$4.14 

$6.17 

$9.33 

$9 67 

$10 9? 

Arch masonry 8.00 “ “ “.. 

2.30 

4.06 

6.72 

10.06 

14 55 

Paving @ 2.00 “ “ “. 

.17 

.25 

.40 

.54 

69 

Excavation .25 “ “ “. 

.23 

.27 

.35 

.39 

.45 

Total cost of 1 additional foot. 

$6.84 

$10.75 

$16.80 

$20.66 

$26.66 







































ART. 3 .] 


ARCH CULVERTS. 


437 


Topeka and Santa Fe*s standard semi-circular arch culvert as given 
in Plate IV and Table 51 (page 430). The excavation is only ap¬ 
proximate, and is computed on the assumption of a pit 2 feet 2 
inches deep for the entire foundation including the paved area; i. e., 
the excavation is computed on the same basis as the two preceding. 
Notice that this culvert is 23 feet between the outer faces of the 
end walls, and hence is 1 foot shorter than that of Table 54 and 2J 
feet shorter than that of Table 55. 

TABLE 56. 

Cost of A. T. and S. F. Semi-circular Arch Culverts 20 Ft. Long 
from Inside to Inside of the Coping, and also of each Addi¬ 
tional Foot of Length. 

FOR DESCRIPTION SEE PAGE 429. 

This table does not include the masonry in the footings. 


Items. 

Span. 

6 ft. 

8 ft. 

10 ft. 

12 ft. 

14 ft. 

16 ft. 

Plain masonry @ $7.00 per cu. yd. 
Arch masonry 8.00 “ “ “ 

Paving “ 2.00 “ “ “ 

Excavation “ .25 “ “ “ 

$325.15 

140.72 

9.88 

6.93 

$766.42 

197.28 

13.15 

13.51 

$997.14 

270.32 

16.42 

16.01 

$1,071.42 

356.04 

19.68 

18.21 

$1,328.12 

418.40 

22.99 

21.10 

$1,785.91 

516.48 

26.26 

24.44 

Total cost of culvert 20 ft. long. 

$482.68 

$990.36 

$1,299.89 

$1,465.35 

$1,790.61 

$2,353.09 

Cost of an Additional Foot 
of Length: 

Plain masonry $7.00 per cu. yd. 

Arch masonry “ 8.00 “ “ “ 

Paving “ 2.00 “ “ “ 

Excavation “ .25 “ “ “ 

$5.44 

6.12 

.52 

.28 

$8.49 

8.58 

.69 

.32 

$11.66 

11.75 

.86 

.40 

$12.44 

15.48 

1.04 

.44 

$14.98 

18.19 

1.21 

.48 

$19.48 

22.46 

1.38 

.54 

Total cost of 1 additional foot 

$12.36 

$18.08 

$24.68 

$29.50 

$34.86 

$43.86 


659. A., T. and S. F. Segmental Culverts. Table 57 is similar to 
the three preceding, and is given to facilitate estimating the cost of 
segmental arch culverts of the standard form employed by the 
Atchison, Topeka and Santa Fe Railroad, as shown in Plate V and 
Table 52 (page 431). The excavation is only approximate, and is 
computed on the assumption of a pit 2 feet 2 inches deep over the 
entire foundation, including the paved area. Notice that this 
culvert is 23 feet between the outer faces of the end walls, and is 
therefore the same length as that of Table 56. 


































438 


CULVERTS. 


[chap. xvil. 


TABLE 57. 

Cost of A. T. and S. F. Segmental Arch Culverts 20 Ft. Long 
from Inside to Inside of the Coping, and also of each Addi* 
tional Foot of Length. 

FOR DESCRIPTION SEE PAGE 429. 

This table does not include the masonry in the footings. 


Items. 

Span. 

6 ft. 

8 ft. 

10 ft. 

12 ft. 

14 ft. 

16 ft. 

Plain masonry @ $7.00 per cu. yd . 

Arch masonry “ 8.00 “ “ “ . 

Paving “ 2.00 “ “ “ . 

Excavation “ .25 “ “ “ . 

$183.45 

99.18 

9.88 

7.33 

$470.34 

150.33 

13.15 

11.75 

$607.99 

190.99 

16.42 

14.11 

$657.83 

229.12 

19.68 

15.17 

$641.41 

298.64 

22.99 

16.45 

9 

$669.13 
353.84 
26.26 
17.8£ 

Total cost of culvert 20 feet long. ... 

$299.84 

$645.57 

$829.51 

$921.80 

$979.49 

$1,067. OS 

Cost of an Additional Foot of 
Length: 

Plain masonry (& $7.00 per cu. yd . 

Arch masonry “ 8.00 “ “ “ . 

Paving “ 2.00 “ “ “ . 

Excavation “ .25 “ “ “ . 

$5.44 

4.31 

.52 

.31 

$9.73 

6.54 

.69 

.39 

$12.96 

8.30 

.86 

.46 

$13.61 

9.96 

1.04 

.50 

$14.47 

12.98 

1.21 

.56 

$14.56 

15.38- 

1.38- 

.62 

Total cost, of 1 additional foot . 

$10.58 

$17.35 

$22.58 

$25.11 

$29.22 

$31.94 



660. Standard Arch Culvert. Table 58 is given to facilitate the 
estimation of the cost of culverts of the general form shown in Plate 
YI. The prices are about the average for the respective kinds of 
work; but in case it is desired to determine the cost for other prices, 

•TABLE 58. 

Cost of Standard Arch Culverts 20 Ft. Long from Inside to Inside 
of the Coping, and of each Additional Foot of Length. 

FOR DESCRIPTION SEE PAGE 429. 

The masonry in the footings is not included in this table. 


Items. 

Span. 

6 ft. 

8 ft. 

10 ft. 

12 ft. 

14 ft. 

16 ft. 

Plain masonry @ $7.00 per cu. yd — 

Arch masonry “ 8.00 “ “ “- 

Paving “ 2.00 “ “ “ 

Excavation “ .25 “ “ “_ 

$233.11 

65.87 

6.83 

8.24 

$330.88 
92.72 
9.84 
9 53 

$496.79 

127.33 

12.65 

12.42 

$683.55 

184.00 

15.47 

15.42 

$912.45 

238.64 

18.28 

18.33 

$1,193.35 

305.62 

20.09 

20.61 

Total cost of culvert 20 feet long ... 

$314.05 

$442.97 

$649.19 

$898.44 

$1,187.70 

$1,539.67 

Cost of an Additional Foot of 
Length : 

Plain masonry (§1 $7.00 per cu. yd_ 

Arch masonry “ 8.00 “ “ “_ 

Paving “ 2.00 “ “ “.... 

Excavation “ .25 “ “ “_ 

$3.88 

2.86 

.37 

.21 

$6.56 

4.03 

.52 

.26 

$9.85 

5.54 

.67 

.31 

$14.00 

8.00 

.81 

.36 

$18.75 

10.38 

.96 

.41 

$24.28 

13.29 

1.11 

.46 

Total cost of 1 additional foot.. 

$7.32 

$11.37 

$16.37 

$23.17 

$30.50 

$39.14 












































































ART. 3 .] 


ARCH CULVERTS. 


439 


it is only necessary to increase or decrease the tabular numbers 
proportionally. The quantities of excavation are, approximately, 
averages of the actual amounts for a number of similar culverts, 
and are equivalent to a pit 2 feet 2 inches deep and of an area equal 
to.the area of the foundation. Notice that the culvert in Table 58 
is 23 feet between the outer faces of the end walls; and is therefore 
the same length as that in Tables 56 and 57, and is 1 foot shorter 
than that of Table 54 and 2^ feet shorter than that of Table 55. 
Notice also that in Table 58 the height of the opening is in each 
case half of the span (see Table 53, page 433), while in Tables 56 
and 57 the height of the opening is nearly the same for all spans 
(see Tables 51 and 52, pages 430, 431). 



CHAPTER XVIII. 


ARCHES. 

661. Definitions. Parts of an Arch. Vonssoirs. The wedge- 

shaped stones of which the arch is composed ; also called the arch¬ 
stones. 

Keystone. The center or highest voussoir or arch-stone. 

Soffit. The inner or concave surface of the arch. 

Intrados. The concave line of intersection of the soffit, with a 
vertical plane perpendicular to the axis or length of the arch. See 
Fig. 110. 

Extrados. The convex curve, in the same plane as the intrados, 
which bounds the outer extremities of the joints between the 
voussoirs. 

Crown. The highest part 
of the arch. 

SkeiobacJc. The inclined 
surface or joint upon which 
the end of the arch rests. 

Abutment. A skewback 
and the masonry which sup¬ 
ports it. 

Springing Line. The in¬ 
ner edge of the skewback. 

Springer. The lowest voussoir or arch-stone 

Haunch. The part of the arch between the crown and the 
skewback. 

Spandrel. The space between the extrados and the roadway. 
The material deposited in this space is called the spandrel filling , 
and may be either masonry or earth, or a combination of them. In 
large arches it often consists of several walls running parallel with 
the roadway, connected at the top by small arches or covered with 
fiat stones, which support the material of the roadway. 



Fig. 110. 


440 















KINDS OF ARCHES. 


441 


a Span, The perpendicular distance between the springing 
lines. 

Rise. The vertical distance between the highest part of the 
intrados and the plane of the springing lines. 

Ring Stones. The voussoirs or arch-stones which show at the 
ends of the arch. 

Arch Sheeting. The voussoirs which do not show at the end 
of the arch. 

Baching. Masonry, usually with joints horizontal or nearly 
so, carried above the skewbacks and outside of the extrados. 

String Course. A course of voussoirs extending from one end 
of the arch to the other. 

Coursing Joint. The joint between two adjoining string 
courses. It is continuous from one end of the arch to the 
other. 

Heading Joint . A joint in a plane at right angles to the axis 
of the arch. It is not continuous. 

Ring Course. The stones between two consecutive series of 
heading joints. 

662. Kinds of Arches. Circular Arch. One in which the 
intrados is a part of a circle. 

Semi-circular Arch. One whose intrados is a semi-circle; also 
called a full-centered arch. 

Segmented Arch. One whose intrados is less than a semi¬ 
circle. 

Elliptical Arch. One in which the intrados is a part of an 
ellipse. 

Basket-Handle Arch. One in which the intrados resembles a 
semi-ellipse, hut is composed of arcs of circles tangent to each 
other. 

Pointed Arch. One in which the intrados consists of two arcs 
of equal circles intersecting over the middle of the span. For ex¬ 
ample, see Figs. 115 and 117, page 447. 

Hydrostatic Arch. An arch in equilibrium under the vertical 
pressure of water. 

Geo static Arch. An arch in equilibrium under the vertical 
pressure of an earth embankment. 

Catenarian Arch. One whose intrados is a catenary. 

663. Right Arch. A cylindrical arch, either circular or el- 



442 


ARCHES. 


[CHAP. XVIII. 


liptical, terminated by two planes, termed heads of the arch, at 
right angles to the axis of the arch. See Fig. 111. 



Shew Arch. One whose heads are oblique to the axis. See 
Fig. 112. Skew arches are quite common in Europe, but are 
rarely employed in the United States; and in the latter when 
an oblique arch is required, it is usually made, not after the 
European method with spiral joints as shown in Fig. 112, but 
by building a number of short right arches or ribs in contact 
with each other, each successive rib being placed a little to one 
side of its neighbor. 

Groined and Cloistered Arches. Those formed by the in¬ 
tersection of two or more cylindrical arches. The spans of 
the intersecting arches may be different, but the rise must be 
the same in each; and their axes must lie in the same plane, 
but may intersect at any angle. The groined arch is formed 
by removing those portions of each cylinder which lie under 
the other and between their common curves of intersection, 
thus forming a projecting or salient angle on the soffit along 
these curves. The cloistered arch is formed by removing those 
portions of each cylinder which are above the other and exterior 
to their common intersection, thus forming re-entrant angles 
along the same lines. 

Dome and Vault. If an arch revolves around a vertical 
through the keystone, a dome is produced; and if it moves in 
a straight line on the springer, a vault is produced. Hence 
there are essentially the same kinds of domes and vaults as 
arches. 

Only right arches will he considered in this cha'pter . 
































LIKE OF RESISTANCE. 


443 


664. Line of Resistance. If the action and reaction between 
each pair of adjacent arch-stones be replaced by single forces so 
situated as to be in every way the equivalent of the distributed 
pressures, the line connecting the points of application of these 
several forces is the line of resistance of the arch. For example, 
assume that the half arch shown in Fig. 113 is held in equilibrium 
by the horizontal thrust T —the reaction of the right-hand half of the 
arch—applied at some point a in the joint CF. Assume also that the 


Fig. 113. 



several arch-stones fit mathematically, and that there is no adhesion 
of the mortar. The forces F x ,F^,F %i and F i represent the result¬ 
ants of all the forces (including the weight of the stone itself) acting 
upon the several voussoirs. The arch-stone CIHF is in equilib¬ 
rium under the action of the three forces, T\ F x , and the reaction 
of the voussoir IHEG. Hence these three forces must intersect 
in a point, and the direction of R —the resultant pressure be¬ 
tween the voussoirs CIHF and IHEG —can be found graphically 
as shown in Fig. 113. The point of application of A, is at b— 
the point where R } intersects the joint HI. The voussoir GEHl 











444 


ARCHES. 


[CHAP. XVIII. 


is in equilibrium under the action of , and i? 2 —the resultant 

reaction between GEHI and GEDH, —and hence the direction, 
the amount, and the point of application ( c ) of R 2 can be deter* 
mined as shown in the figure, island R 4 are determined in the same 
manner as R x and R 2 . 

The points a, b, c, cl, and e, called centers of pressure, are the 
points of application of the resultants of the pressure on the several 
joints ; or they may be regarded as the centers of resistance for the 
several joints. In the latter case the line abccle would be called 
the line of resistance, and in the former the line of pressure . 
Strictly speaking, the line of resistance is a continuous curve cir¬ 
cumscribing the polygon abcde. The greater the number of 
joints the nearer the polygon abccle approaches this curve. Occa¬ 
sionally the polygon mnop is called the line of resistance. The 
greater the number of joints the nearer this line approaches the 
line of resistance as defined above. For an infinite number of joints 
the polygons abccle and mnop coincide with the curved line of re¬ 
sistance, a, b, c, cl, and e being common to all three. 

Notice that if the four geometrical lines ab, be, cd, and de were 
placed in the relative position shown in Fig. 113, and were acted 
upon by the forces T, F x , F i} F % , F 4 , and R, as shown, they would 
be in equilibrium ; and hence the line abcde, or rather a curve 
passing through the points a, b, c, d, and e, is sometimes called a 
linear arch. 


Art. 1. Theory of the Arch. 

665. The theory of the masonry arch is one of great com¬ 
plexity. Numerous volumes have been written on this subject, and 
it still occupies the attention of mathematicians. No attempt will 
be made here to give an exhaustive treatise on the arch ; but the 
fundamental principles will be stated as clearly as possible, and the 
principal solutions of the problem which have been proposed from 
time to time will be explained and their underlying assumptions 
pointed out. 

666. Tjie External Forces. It is clear that before we can 
find the strains in a proposed arch and determine its dimensions, 
we must know the load to be supported by it. In other words, 
the strength and stability of a masonry arch depend upon the 



ART. 1.] 


THEORY OF THE ARCH. 


445 


position of the line of resistance ; and before this can be deter¬ 
mined, it is necessary that the external forces acting upon the arch 
shall be fully known, i. e., that (1) the point of application, (2) the 
direction, and (3) the intensity of the forces acting upon each 
voussoir shall be known. Unfortunately, the accurate determina¬ 
tion of the outer forces is, in general, an impossibility. 

1. If the arch supports a fluid, the pressure upon the several 
voussoirs is perpendicular to the extrados, and can easily be found ; 
and combining this with the weight of each voussoir gives the 
several external forces. This case seldom occurs in practice. 

2. If the arch is surmounted by a masonry wall, as is frequently 
the case, it is impossible to determine, with any degree of accuracy, 
the effect of the spandrel walls upon the stability of the arch. It, 
is usually assumed that the entire weight of the masonry above the 
soffit presses vertically upon the arch; but it is known certainly 
that this is not the case, for with even dry masonry a part of the 
wall will be self-supporting. The load supported by the arch can 
be computed roughly by the principle of § 250 (p. 168); but, as this 
gives no idea of the manner in which this pressure is distributed, it 
is of but little help. The error in the assumption that the entiro 
weight of the masonry above the arch presses upon it is certainly on 
the safe side; but if the data are so rudely approximate, it is use¬ 
less to attempt to compute the strains by mathematical processes. 
The inability to determine this pressure constitutes one of the limi¬ 
tations of the theory of the arch. 

Usually it is virtually assumed that the extradosal end of each 
voussoir terminates in a horizontal and vertical surface (the latter 
may be zero); and therefore, since the masonry is assumed to press 
only vertically, there are no horizontal forces to be considered. But 
as the extrados is sometimes a regular curve, there would be active 
horizontal components of the vertical pressure on this surface; and 
this would be true'even though the spandrel masonry were divided 
by vertical joints extending from the extrados to the upper limit of 
the masonry. Further, even though no active horizontal forces are 
developed, the passive resistance of the spandrel masonry—either 
spandrel walls or spandrel backing—materially affects the stability 
of an arch. Experience shows that most arches sink at the crown 
and rise at the haunches when the centers are removed (see Fig. 
116, p. 44?), and hence the resistance of the spandrel masonry will 



446 


ARCHES. 


[chap. xvitl 


materially assist in preventing the most common form of failure. 
The efficiency of this resistance will depend upon the execution of 
the spandrel masonry, and will increase as the deformation of the 
arch ring increases. It is impossible to compute, even roughly, the 
horizontal forces due to the spandrel masonry. 

Further, in computing the strains in the arch, it is usually 
assumed that the arch ring alone supports the masonry above it; 
while, as a matter of fact, the entire masonry from the intrados to 
the top of the wall acts somewhat as an arch in supporting its own 
weight. 

3. If the arch supports a mass of earth, we can know neither the 
amount nor the direction of the earth pressure with any degree of 
accuracy (see Chap. XIV—Retaining Walls,—particularly § 527, 
page 339). We do know, however, that the arch does not support 
the entire mass above it (see §§ 618-20). No one ever thinks of 
trying to make a tunnel arch strong enough to sustain the weight of 
the entire mass above it. 

In the theory of the masonry arch, the pressure of the earth is 
usually assumed to be wholly vertical. That the pressure of earth 
gives, in general, active horizontal forces appears to be unquestion¬ 
able. An examination of Fig. 113 (page 443) will show how the 
horizontal forces add stability to an arch ring whose rise is equal to 
or less than half the span. It is clear that for a certain position 
and intensity of thrust T, the line of resistance will approach the 
extrados nearer when the external forces are vertical than when 
they are inclined. We know certainly that the passive resistance of 
the earth adds materially to the stability of masonry arches ; for the 
arch rings of many sewers which stand without any evidence of 
weakness are in a state of unstable equilibrium, if the vertical press¬ 
ure of the earth immediately above it be considered as the only 
external force acting upon it. 

667. Method of Failure of Arches. A masonry arch may 
yield in any one of three ways, viz.: (1) by the crushing of the 
stone, or (2) by the sliding of one voussoir on another, or (3) by 
rotation about an edge of some joint. 1. An arch will fail if the 
pressure on any part is greater than the crushing strength of the 
material composing it. 2. Figs. 114 and 115 represent the second 
method of failure; in the former the haunches of the arch slide 



ART. 1.] 


THEORY OF THE ARCH. 


44 ? 


out and the crown slips down, and in the latter the reverse is 
shown. If the rise is less than the span and the arch fails by the 
sliding of one voussoir on the other, the crown will usually sink; 
but if the rise is more than the span, the haunches will generally 




he pressed inward and the crown will rise. 3. Figs. 116 and 117 
show the two methods by which an arch may give way by rotation 



Fig.116. 


Fig. 117. 


about the joints. As a rule the first case is most frequent for flat 
arches and the second for pointed ones. 

However, more arches fail on account of unequal settlement of 
the foundation than because of a faulty design of the arch proper. 

668. CRITERIA OF Safety. There are three criteria, corre¬ 
sponding to the three modes of failure, by which the stability of an 
arch may be judged. (1) To prevent overturning, it is necessary 
that the line of resistance shall everywhere lie between the intrados 
and the extrados. (2) To prevent crushing, the line of resistance 
should intersect each joint far enough from the edge so that the 
maximum pressure will be less than the crushing strength of the 
masonry. (3) To prevent sliding, the angle between the line of 
resistance and the normal to any joint should be less than the angle 
of repose (“angle of friction”) for those surfaces; that is to say, 
the tangent of the angle between the line of resistance and the 
normal to any joint should be less than the co-efficient of friction 
(§ 489). 







448 


ARCHES. 


[CHAP. XVIII. 


669. Stability against Rotation. An arch composed of incom¬ 
pressible voussoirs can not fail by rotation as shown in Fig. 116, 
unless the line of resistance touches the intrados at two points and 
the extrados at one higher intermediate point (see Fig. 120, page 
454); and an arch can not fail by rotation as shown in Fig. 117, 
unless the line of resistance touches the extrados at two points 
and the intrados at one higher intermediate point (see Fig. 120). 
The factor of safety against rotation about any point is equal 
to half the length of the joint divided by the distance between 
the center of pressure and the center of the joint ; that is to 
say. 


the factor of safety = 


ii 

d 9 



in which l is the length of the joint and d the distance between 
the center of pressure and the center of the joint. For example, if 
the center of pressure is at one extremity of the middle third of the 
joint, d = £ l ; and, by equation (1), the factor of safety is three. 
If the center of pressure is £ l from the middle of the joint, the 
factor of safety is two. 

It is customary to require that the line of resistance shall lie 
within the middle third of the arch ring, which is equivalent to 
specifying that the minimum factor of safety for rotation shall not 
be less than three. 

670. Stability against Crushing. The method of determining 
the pressure on any part of a joint has already been discussed in the 
chapter on masonry dams (see pp. 320-26). When the total press¬ 
ure and its center are known, the maximum pressure at any part 
of the joint is given by formula (23), page 323. It is 


P = 


w e wd 

i ' r 9 



in which P is the maximum pressure on the joint per unit of area ; 
W is the total normal pressure on the joint per unit of length of the 
arch ; l is the depth of the joint, i. e., the distance from intrados to 
extrados ; and d is the distance from the center of pressure to 
the middle of the joint. This formula is general, provided the 






ART. l.J 


THEORY OF THE ARCH. 


449 


masonry is capable of resisting tension ; and if the masonry is 
assumed to be incapable of resisting tension, it is still general, pro¬ 
vided d does not exceed -J- /. 

For the case in which the masonry is incapable of resisting ten¬ 
sion and d exceeds -jt /, the maximum pressure is given by formula 
(24), page 324. It is 


P = 


2 W 

3 (il-d) 



If the line of resistance for any arch can be drawn, the maximum 
pressure can be found by (1) resolving the resultant reaction per¬ 
pendicular to the given joint, and (2) measuring the distance d from 
a diagram of the arch similar to Fig. 113 (page 443), and (3) sub¬ 
stituting these data in the proper one of the above formulas (the 
one to be employed depends upon the value of d), and computing 
P* This pressure should not exceed the compressive strength of 
the masonry. 

It is customary to prescribe that the line of resistance shall lie 
within the middle third of each joint, and also that the result 
obtained by dividing the total pressure by the area of the joint shall 
not be more than one twentieth of the ultimate crushing strength 
of the stone. Under these conditions the maximum pressure is 
twice the mean, and hence using the above limits is equivalent to 
saying that the maximum pressure shall not be more than one tenth 
of the ultimate crushing strength of the stone. The mean pressure 
in arches is usually not more than one fortieth or one fiftieth, and 
sometimes only one hundredth, of the ultimate compressive strength 
of the stone or brick of which it is constructed. 

671. Unit Pressure. In the present state of our knowledge it 
is not possible to determine the value of a safe and not extravagant 
unit working-pressure. The customary unit appears less extrava¬ 
gant, when it is remembered (1) that the crushing strength of 
masonry is considerably less than that of the stone or brick of which 
it is composed (see §§ 221-22 and §§ 246-47 respectively), and that 
we have no definite knowledge concerning either the ultimate or 
the safe crushing strength of stone masonry (§ 223) and but little 


* For a numerical example of the method of doing this, see 2, § 690. 








450 


ARCHES. 


[CHAP. XVIII. 


concerning that of brickwork (§ 248) ; and (2) that all the data we 
have on crushing strength are for a load perpendicular to the 
pressed surface, while we have no experimental knowledge of the 
effect of the component of the pressure parallel to the surface of the 
joint, although it is probable that this component would have some¬ 
what the same effect upon the strength of the voussoirs as a sheet 
of lead has when placed next to a block of stone subjected to com¬ 
pression (§12). 

On the other hand, there are some considerations which still 
further increase the degree of safety of the usual working-pressure. 
(1) When the ultimate crushing strength of stone is referred to, the 
crushing strength of cubes is intended, although the blocks of stone 
employed in actual masonry have less thickness than width, and 
hence are much stronger than cubes (see § 15, paragraph 2 § 60, and 
§ 273). To prevent the arch stones from flaking off at the edges, 
the mortar is sometimes dug out of the outer edge of the joint. 
This procedure diminishes the area under pressure, and hence 
increases the unit pressure ; but, on the other hand, the edge of 
the stone which is not under pressure gives lateral support to the 
interior portions, and hence increases the resistance of that portion 
(see § 273). It is impossible to compute the relative effect of these 
elements, and hence we can not theoretically determine the efficiency 
of thus relieving the extreme edges of the joint. (2) The preceding 
formulas (2 and 3) for the maximum pressure neglect the effect of 
the elasticity of the stone ; and hence the actual pressure must be 
less, by some unknown amount, than that given by either of the 
formulas. 

672. Notice that the distance which the center of pressure may 
vary from the center of the joint without the masonry's being 
crushed depends upon the ratio between the ultimate crushing 
strength and The mean pressure on the joint. In other words, if 
the mean pressure is very nearly equal to the ultimate crushing 
strength, then a slight departure of the center of pressure from the 
center of the joint may crush the voussoir; but, on the other hand, 
if the mean pressure is small, the center of pressure may de¬ 
part considerably from the center of the joint without the stone's 
being crushed. This can be shown by equation (2), page 448. 
W 

If both P and — are large, d must be small; but if P is large and 




•ART. 1.] 


THEORY OF THE ARCH, 


451 


w 

small, then d may be large. 

L 


Essentially the same result can be 


deduced from equation (3), page 449. 

Even though the line of resistance approaches so near the edge 
of the joint that the stone is crushed, the stability of the arch is not 
necessarily endangered. For example, conceive a block of stone 
resting upon an incompressible plane, 

AB, Fig. 118, and assume that the 
center of pressure is at N. Then the n 
pressure is applied over an area pro¬ 
jected in A V, such that AN — ^ A V. 

The pressure at A is represented by * 

AKy and the area of the triangle 
AKV represents the total pressure on the joint. Assume that 
AK is the ultimate crushing strength of the stone, and that the 
center of pressure is moved to N'. The pressure is borne on an 
area projected in A V'. The pressure in the vicinity of A is 
uniform and equal to the crushing strength A K ; and the total 
pressure on the joint is represented by the area of the figure 
A K G V'y which has its center of gravity in the vertical 
through N '. Eventually, when the center of pressure approaches 
so near A that the area in which the stone is crushed becomes 
too great, the whole block will give way and the arch will 
fall. * 

673. Open Joints. It is frequently prescribed that the line of 
resistance shall pass through the middle third of each joint, “ so 
that the joint may not open on the side most remote from the line 
of resistance.” If the line of resistance departs from the middle 
third, the remote edge of the joint will be in tension ; but since 
cement mortar is now quite generally employed, if the masonry is 
laid with ordinary care the joint will be able to bear considerable 
tension (see Table 13, page 94); and hence it does not necessa¬ 
rily follow that the joint will open. 



* Rankine says: “ It is true that arches have stood, and still stand, in which the 
centers of resistance of joints fall beyond the middle third of the depth of the arch 
ring; but the stability of such arches is either now precarious, or must have been 
precarious while the mortar was fresh.” The above is one reason why the stability 
of the arch is not necessarily precarious, and other reasons are found in § 666 and 
also in the subsequent discussion. A reasonable theory of the arch will not make a 
structure appear instable which shows every evidence of security. 








452 


ARCHES. 


[CHAP. XYIII. . 


If the line of pressure departs from the middle third and the 
mortar is incapable of resisting tension, the joint will open on the 
side farthest from the line of resistance. For example, if the 
center of pressure is at N, Fig. 118, then a portion of the joint 
A V ( — 3 AA^) is in compression, while the portion VB has no force 
acting upon it ; and hence the yielding of the portion A Fwill cause 
the joint to open a little at B . This opening will increase as the 
center of pressure approaches A, and when the material at that 
point begins to crush the increase will become comparatively rapid. 

Notice that if there are open joints in an arch, it is certain 
that the actual line of resistance does not lie within the middle 
third of such joints. Notice, however, that the opening of a joint 
does not indicate that the stability of the arch is in danger. In 
most cases, an open joint is no serious matter, particularly if it is in 
the soffit. If in the extrados, it is a little more serious, since water 
might get into it and freeze. To guard against this danger, it is 
customary to cover the extrados with a layer of puddle or some 
coating impervious to water (§ 264). 

674. Stability against Sliding. If the effect of the mortar is 
neglected, an arch is stable against sliding when the line of resist¬ 
ance makes with the normal an angle less than the angle of friction. 
According to Table 36 (page 315) the co-efficient of friction of 
masonry under conditions the most unfavorable for stability—/. e., 
while the mortar is wet—is about 0.50, which corresponds to an angle 
of friction of about 25°. Hence if the line of pressure makes an 
angle with the normal of more than 25°, there is a possibility of 
one voussoiFs sliding on the other. This possibility can be elimi¬ 
nated by changing the joints to a direction more nearly at right 
angles to the line of pressure. 

However, there is no probability that an arch will receive its full 
load before the mortar has begun to set; and hence the angle of 
friction is virtually much greater than 25°. It is customary to 
arrange the joints of the arch at least nearly perpendicular to the 
line of resistance, in which case little or no reliance is placed on the 
resistance of friction or the adhesion of the mortar. 

675. Conclusion. From the preceding discussion, it will be 
noticed that the factors of stability for rotation and for crushing 
are dependent upon each other ; while the factor for sliding is 
independent of the other conditions of failure, and is dependent 




ART. 1.] 


THEORY OF THE ARCH. 


453 


only upon tlie direction given to the joints. A theoretically perfect 
design for an arch would he one in which the three factors of safety 
were equal to each other and uniform throughout the arch. As 
arches are ordinarily built, the factor for rotation is about three, or 
a little more ; the nominal factor for crushing is ten to forty; and 
the nominal factor for sliding is one and a half to two. 

It is evident that before any conclusions can be drawn concern¬ 
ing the strength or stability of a masonry arch, the position of the 
line of resistance must be known ; or, at least, limits must be found 
within which the true line of resistance must be proved to lie. 

676. Location of the True Line of Resistance. The de¬ 
termination of the line of resistance of a semi-arch requires that the 
external forces shall be fully known, and also that (1) the amount, 
(2) the point of application, and (3) the direction of the thrust at 
the crown shall be known. The determination of the external 
forces is a problem independent of the theory of the arch ; and for 
the present it will be assumed that they are fully known, although 
as a matter of fact they can not be known with any considerable 
degree of accuracy (see § 666). 

Each value for the intensity of the thrust at the crown gives a 
different line of resistance. For example, in Fig. 113 (page 443), 
if the thrust T be increased, the point i —where R l intersects the 
plane of the joint HI —will approach /; and consequently c, cl, 
and e will approach G, H, and A respectively. If T be increased 
sufficiently, the line of pressure will pass through A or H (usually 
the former, this depending, however, upon the dimensions of the 
arch and the values and directions of F 1 , F i9 and jF 3 ), and the arch 
will be on the point of rotating about the outer edge of one of these 
joints. This value of T is then the maximum thrust at a consistent 
with stability of rotation about the outer edge of a joint, and the 
'Corresponding line of resistance is the line of resistance for maxi¬ 
mum thrust at a. Similarly, if the thrust ^be gradually decreased, 
the line of resistance will approach and finally intersect the intrados, 
in which case the thrust is the least possible consistent with stabil¬ 
ity of rotation about some point in the intrados. The lines of 
resistance for maximum and minimum thrust at a are shown in 
Fig. 119 (page 454). 

If the point of application of the force T be gradually lowered 
and at the same time its intensity be increased, a line of resistance 




454 


ARCHES. 


[chap, xyiih 



/Z'f' 
</ 


may be obtained which will have one point in common with the- 

intrados. This is the line of resistance for 
maximum thrust at the crown joint. Simi¬ 
larly, if the point of application of T be 
gradually raised, and at the same time its 
intensity be decreased, a line of resistance 
may be obtained which will have one point 
in common with the extrados. This is the 
line of resistance for minimum thrust at 
the crown joint. The lines of resistance 
for maximum and minimum thrust at the crown are showm in 
Fig. 120. 

Similarly each direction of the 
thrust T will give a new line of re¬ 
sistance. In short, every different 
value of each of the several factors, 
and also every combination of these 
values, will give a different position j ^ 
for the line of resistance. Hence, the / A/ 
problem is to determine which of the 
infinite number of possible lines of 
resistance is the actual one. This 
problem is indeterminate, since there are more unknown quantities 
than conditions (equations) by which to determine them. To 
meet these difficulties and make a solution of the problem possible, 
various hypotheses have been made ; but there is no unanimity of 
opinion among authorities regarding the position of the true line 
of resistance. Some of these hypotheses will now be considered 
briefly. 

677. Hypothesis of Least Pressure. Some writers have assumed 
the true line of resistance to be that which gives the smallest abso¬ 
lute pressure on any joint. This principle is a meta-physical one, 
and leads to results unquestionably incorrect. Of the four hypo¬ 
theses here discussed this is the least satisfactory, and the least 
frequently employed. It will not be considered further. 

For an explanation of Claye’s method of drawing the line of 
pressure according to this theory, see Van Nostrand ? s Engineering 
Magazine, vol. xv, pp. 33-36. For a general discussion of the 
theory of the arch founded on this hypothesis, see an article by Pro- 


Fig. 120. 








-aRT. 1.] 


THEORY OF THE ARCH. 


455 


fessor Du Bois in Van ISTostrand's Engineering Magazine, vol. xiii, 
pp. 341-46, and also Du Bois’s “Graphical Statics,” Chapter XV. 

678. Hypothesis of Least Thrust at the Crown. According to 
this hypothesis the true line of resistance is that for which the 
thrust at the crown is the least possible consistent with equilibrium. 
This assumes that the thrust at the crown is a passive force called 
into action by the external forces ; and that, since there is no need 
for a further increase after it has caused stability, it will be the least 
possible consistent with equilibrium. 

This principle alone does not limit the position of the line of 
resistance; but, if the external forces are known and the direction 
of the thrust is assumed, this hypothesis furnishes a condition by 
which the line of resistance corresponding to a minimum thrust can 
be found by a tentative process. The principle of least crown 
thrust w'as first proposed by Moseley,*' was amplified by Scheffler,f 
and has been adopted more generally 
by writers and engineers than any 
other. 

679. The portion of the arch shown 
in Fig. 121 is held in equilibrium by (1) 
the vertical forces, w x , w 2 , etc., (2) by 
the horizontal forces h x , h 2 , etc., (3) by 
the reaction R at the abutment, and (4) 
by the thrust T at the crown. The 
direction of R is immaterial in this 
discussion. Let a and b represent the points of application of T 
and R, respectively, although the location of these points is yet un¬ 
determined. Let 

T — the thrust at the crown; 

x x = the horizontal distance from b to the line of action of u\; 
x a = the same for u\, etc.; 



* Philosophical Magazine, Oct., 1833—see Moseley’s Mechanical Principles of En¬ 
gineering, 2d American ed., p. 430. 

+ “ Theorie der Gewolbe, Futtermauern, und eisernen Briicken,” Braunschweig, 
1857. A French translation of this work is entitled “ Traits de la Stability des con¬ 
structions ; Ire partie, Thdorie des Voutes et des Murs de Soutenement,” Paris, 1864. 
Cain’s “ A Practical Theory of Voussoir Arches No. 12 of Van Nostrand’s Science 
Series—New York, 1874, is an exposition of a theory of the arch based upon this 
hypothesis. 









456 


ARCHES. 


[CHAP. XVIII. 


y = the perpendicular distance from b to the line of action of T\ 
k x — the perpendicular distance from b to the line of action of 
h x ; k 9 = the same for A 2 ; etc. 

. Then, by taking moments about b, we have 

Ty — iu l x x + ^^ 2 z 2 + etc. -j- h x k x + A 2 & 2 -f etc.; . (4) 

hence 


T = 


2 ID X 

y 


+ 


2 hk 

y 



1. The value of T depends upon 2 h k —the sum of the 
moments of the horizontal component of the external forces;—but 
we know neither the nature of the material over the arch nor the 
value of 2 h k for any particular material (see §§ 527-31). In 
discussing and applying this principle, the term 2 h k is usually 
neglected. Ordinarily this gives an increased degree of stability; 
but this is not necessarily the case. The omission of the effect of 
the horizontal component makes the computed value of Tless than 
it really is, and causes the line of resistance found on this assump¬ 
tion to approach the inlrados at the haunches nearer than it does in 
fact; and hence the conditions may be such that the actual line of 
resistance will be unduly near the extrados at the haunches, and 
consequently endanger the arch in a new direction. 

2. For simplicity of discussion, and because the error involved in 
the discussion immediately to follow is immaterial, we will tempo¬ 
rarily omit the effect of the horizontal components of the external 
forces. If the horizontal forces are disregarded, equation (5) 
becomes 


T = 


2 w x 

y 



From equation (6) we see that, other things remaining the same, 
the larger y the smaller T ; and hence, for a minimum value of T, 
a should be as near c as is possible without crushing the stone (see 
§§ 670-72). Usually it is assumed that ac is equal to one third of 
the thickness of the arch at the crown ; and hence, the average 
pressure per unit of area is to be equal to one half of the assumed 
unit working pressure ; or, in other words, twice the thrust T 
divided by the thickness of the crown is to be equal to the unit, 
working pressure. 








ART, 1.] 


THEORY* OF THE ARCH. 


45? 


3. To determine y , it is necessary that the direction of T should 
be known. It is usually ^assumed that Tis horizontal. If the arch 
is symmetrical and is loaded uniformly over the entire span, this 
assumption is reasonable ; but if the arch is subject to heavy moving 
loads, as most are, the thrust at the crown is certainly not hori¬ 
zontal, and can not be determined. 

4. If the joint A B is horizontal, then b is to be taken as near 
A as is consistent with the crushing strength of the stone, or at, 
say, one third of the length of the joints B from A. Notice that 
if the springing line is inclined, as in general it will be (see last 
two paragraphs of § 682, p. 463), moving b toward A decreases x> 
and will at the same time increase y. Hence the position of b cor¬ 
responding to a minimum value of T can be found only by trial. 
It is usual, however, to assume that Ab is one third of AB, what¬ 
ever the inclination of the joint. 

680. Joint of Rupture. The joint of rupture is that joint for 
which the tendency to open at the extrados is the greatest. The 
joint of rupture of an arch is analogous to the dangerous section of 
a beam. Practically, the joint of rupture is the springing line of 
the arch, the arch masonry below that joint being virtually only a 
part of the abutment. 

That no joint may open at the extrados, the thrust at the crown 
must be at least equal to the maximum value of T as determined 
by equation (5), page 456. If the thrust is less than this, the joint 
of rupture will open- at the extrados ; and a greater value is incon¬ 
sistent with the hypothesis of minimum crown thrust. Since the 
moment of the horizontal components of the external forces is 
indeterminable, the position of the true joint of rupture can be 
found only by trial for assumed values and positions of the hori¬ 
zontal forces. 

681. As an example, assume that it is required to determine the 
joint of rupture of the 16-foot arch shown in Fig. 122, which is 
the standard form employed on the Chicago, Kansas & Nebraska 
K. It. (see page 427 and Plate III). Assume that the arch supports, 
an embankment of earth extending 10 feet above the crown, and 
that the earth weighs 100 pounds per cubic foot and the masonry 
160. For simplicity, consider a section of the arch only a foot 
thick perpendicular to the plane of the paper. The half-arch ring 
and the earth embankment above it are divided into eight sections, 



458 


ARCHES. 


[CHAP. XVIII 


which for a more accurate determination of the joint of rupture 
are made smaller near the supposed position of that joint. The 
weight of the first section rests upon the first joint, that of the first 
two upon the second joint, etc. The values and the positions of 



the lines of action of the weights of the several sections are given in 
the second and third columns of Table 59.* 


* The center of gravity of the arch stone is found by the method explained in 
§ 494 (page 318); and the center of gravity of the prism of earth resting upon each arch 
stone may, without sensible error, be taken as acting through its medial vertical line. 
The center of gravity of the combined weight of the arch stone and the earth resting 
upon it may be found by either of the two following methods, of which the first is 
the shorter and more accurate : 

1. The center of gravity of the two masses may be found by the following well- 
known principle of analytical mechanics : 

- tCj aq + w 2 x „ 

x .. 

in which x is the horizontal distance from any point, say the crown, to the vertical 
through the center of gravity of the combined masses, w l and w 2 are the weights of 
the two masses, and x, and x a the horizontal distances from any point, say the crown, 
to the verticals through the centers of gravity of the separate masses respectively. 
The same method can be employed for finding the center of gravity of any number 
of masses, by simply adding the corresponding term or terms in the numerator and 
the denominator of equation (7). 

2. Since the principles employed in the second method of finding the center of 
gravity of each arch stone and its load are frequently employed, in one form or 
























ART. l.J 


THEORY OF THE ARCH. 


459 


TABLE 59. 

To find the Joint of Rupture of the Arch Ring shown in Fig. 122. 


No. of the joint, counting 
from the one next to the 
crown. 

Data for Ver¬ 
tical Forces. 

Data for Hori¬ 
zontal Forces. 

Position of the 
Center of 
Pressure for 
each Joint. 

Thrust at the Crown. 

» 

Amount of the 
force. 

Horizontal dis¬ 
tance of point of 
application from 
the crown joint. 

Amount of the 
force. 

Vertical distance 
of point of appli¬ 
cation from the 
top of the crown 
joint. 

Horizontal dis¬ 
tance from the 
crown joint. 

Vertical distance 
from the top of 
the crown joint. 

2 to x 

2 h k 

Total 

thrust. 

y 

y 


Lbs. 

Feet. 

Lbs. 

Feet. 

Feet. 

Feet. 

Lbs. 

Lbs. 

Lbs. 

1 

2.938 

1.20 

66 

0.10 

2.20 

1.18 

3.866 

94 

3,960 

2 

3,045 

3.57 

243 

0.55 

4.27 

1.86 

7.744 

308 

8,052 

3 

1,644 

5.33 

192 

1.17 

5.27 

2.42 

8,518 

424 

8,942 

4 

1.716 

6.45 

259 

1.78 

6.17 

3.11 

8,74s 

662 

9,4io 

5 

1.825 

7.50 

315 

2.53 

6.98 

3.90 

8,577 

700 

9,277 

6 

1,888 

8.47 

415 

3.40 

7.71 

4.81 

8,407 

941 

9.348 

7 

3,939 

9.77 

1.030 

5.02 

8.85 

6.84 

7,506 

1,407 

8,911 

8 

4,098 

11.05 

1,624 

7.70 

9.50 

9.25 

5,990 

1,983 

7,973 


another, in discussions of the stability of the masonry arch, this method will be ex¬ 
plained a little more fully than is required for the problem in hand. 

The first step is to reduce the actual load upon an arch (including the weight of 
the arch ring itself) to an equivalent homogeneous load of the same density as the 
arch ring. The upper limit of this imaginary loading is called the reduced-load contour. 
For example, suppose it is required to find the reduced-load contour for the arch 
loaded as in Fig. 123. Assume that the weight of the arch ring is 160 pounds per 




cubic foot; that of the rubble backing, 140 ; and that of the earth, 100. Then the 
ordinate at a to the load contour of an equivalent load of the density of the arch ring 

is equal to a b + & c + e d ^ = » say, gf. The value of gf is laid off in Fig. 124. 

160 160 

Computing the ordinates for other points in the load contour gives the line E F, Fig. 
124, which is the reduced-load contour for the load shown in Fig. 123. The area 
between the intrados and the reduced-load contour is proportional to the load on the 
arch. In a similar manner, a live load (as, for example, a train) can be reduced to 
an equivalent load of masonry,—in which case the reduced-load contour would con¬ 
sist of a line G H above and parallel to El for that part of the span covered by the 






































































460 


ARCHES. 


[CHAP. XVIII. 


The value and position of the horizontal components of the 
external forces are somewhat indeterminate (see §§ 528-31). Ac¬ 
cording to Rankings theory of earth pressure,* * the horizontal 

pressure of earth at any point can not be greater than ^ gj^ ^ 

times the vertical pressure at the same point, nor less than 

f^~5n"0 times the vertical pressure,—0 being the angle of 

repose, f If 0 = 30°, the above expression is equivalent to saying 
that the horizontal pressure can not be greater than three times 
the vertical pressure nor less than one third of it. Evidently 
the horizontal component will be greater the harder the earth 
spandrel-filling is rammed into place. The condition in which the 
earth will be deposited behind the arch can not be foretold, but it 
is probable that at least the minimum value, as above, will always 
be realized. Hence we will assume that the horizontal intensity 
is at least one third of the vertical intensity; that is to say, 
h = % edl, in which e is the weight of a cubic unit of earth—which 
was assumed above at 100 pounds ,—d the depth of the center of 
pressed surface below the top of the earth filling, and l the vertical 
dimension of the surface. The values and the positions of the 
horizontal forces acting on the respective sections of the arch ring 
are given in the second double column of Table 59. 


To find the least thrust at the crown consistent with stability of 
rotation, assume that the center of pressure on any joint is at a 
distance from the intrados equal to one third of the length of the 
joint (see paragraph 4, page 457). The co-ordinates to the several 
centers of pressures are given in the third double column of Table 
59. Notice that the several values of x and k are simply the differ¬ 
ences between two quantities given in the table. The thrust at the 
crown is supposed to be applied at the upper limit of the middle 
third of the crown joint. The length of the crown joint is 1.25 feet • 
and hence the several values of y are the respective quantities in the 


train ; while for the remainder of the span, the line IF is the reduced-load contour 
The second step is to draw the arch ring and its reduced-load contour on thick 
paper, to a large scale, and then, with a sharp knife, carefully cut out the area repre¬ 
senting the load on each arch stone. The center of gravity of each piece, as ijk l mn 
Fig. 134, can be found by balancing it on a knife-edge ; and then the position of the 
center of gravity is to be transferred to the drawing of the arch. 

* See § 544, page 348. 

t Rankine’s Civil Engineering, p. 320. 








ftRT. 1.] 


THEORY OF THE ARCH. 


461 


seventh column of Table 59 minus of 1.20 feet. The last three 
columns of the table contain the values of the crown thrust as, 
computed by equation (5), page 456. 

An inspection of the results in the last column of Table 59 
shows that the thrust is a maximum for joint 4. A repetition of 
the computations, using smaller divisions of the arch ring, might 
show that the absolute maximum occurs a little to one side or the 
other of this joint; but the uncertainty in the data for both the 
vertical and the horizontal forces is too great (see § 619 and §§ 527-31 
respectively) to justify an attempt at absolute accuracy, and hence 
we will assume that joint 4 is the true joint of rupture. The 
angular distance of this joint from the crown is 45°, which quantity 
is termed the angle of rupture. 

Any increase in the assumed intensity of the horizontal com¬ 
ponents increases the computed value of the angle of rupture. 
For example, if the quantities in the next to the last column of 
Table 59 be doubled, the thrust for joint 7 will be the maximum. 
Probably this condition could be realized by tightly tamping the 
earth spandrel-filling. 

Notice that the preceding discussion of the position of the 
joint of rupture is for a uniform stationary load. The angle of 
rupture for a concentrated moving load will differ from the results 
found above; but the mathematical investigation of the latter case 
is too complicated and too uncertain to justify attempting it. 

682 . In discussions of the position of the joint of rupture, the 
horizontal components are usually neglected.* This phase of the 
subject will be considered only briefly. The following is the 
method usually employedf in investigating the position of the joint, 
of rupture, and is based on the assumption that the crown thrust is. 
correctly given by equation (6), page 456. 

Let W = the total weight resting on any joint; x — the hori¬ 
zontal distance of the center of gravity of this weight from the 
origin of moments; and y — the arm of the crown thrust. Then 
equation (6) becomes 

T- — 

_ y_ 

* So far as observed, Rankine’s investigation is the only exception; and it is, in 
fact, only an apparent exception (see paragraph 2, page 490). 

fFor example, see Sonnet’s Dictionnaire des Mathdmatique Appliqu6es, pp., 
1084-85. 







462 


ARCHES. 


[CHAP. XYIII. 

To determine the condition for a maximum, it is assumed that IF, 
x 3 and y are independent variables. Differentiating equation (8), 

dT _ 1 d(Wx) _ Wx % 

~dy~ y dy y % ’ 

but d( Wx) — Wdx -|- dW. \ dx — Wdx, and then 

dT _ W dx Wx 

dy~ y dy if . 

Hence the condition for a maximum crown thrust is 

dx _ x 

dy~ y . 

The usual interpretation of equation (10) is: “ The joint of rup¬ 
ture is that joint at which the tangent to the intrados passes 
through the intersection of T and the resultant of all the vertical 
forces above the joint in question.” 

The position of the joint of rupture can be found by the above 
principle only by trial. This method possesses no advantage over 
the one explained in the preceding section, and is less convenient to 
apply. The preceding investigation is approximate for the following 
reasons: 1. The effect of the horizontal forces is omitted. 2. W 9 
x, and yare dependent variables, and not independent as assumed. 
3. In the interpretation of equation (10), instead of “ the tangent 
to the intrados,” should be employed the tangent to the line of 
resistance. 

In applying this method, a table, computed by M. Petit, which 
gives the angle of rupture in terms of the ratio of the radii of the 
intrados and the extrados, is generally employed. The table in¬ 
volves the assumption that a, Fig. 121 (p. 455), is in the extrados 
and b in the intrados; and also that the intrados and extrados are 
parallel. According to this table, “a semi-circular arch of which 
the thickness is uniform throughout and equal to the span divided 
by seventeen and a half is the thinnest or lightest arch that can 
stand. A thinner arch would be impossible.” If the line of re¬ 
sistance is restricted to the middle third, then, according to this 
theory, the thinnest semi-circular arch which can stand is one 
whose span is five and a half times the uniform thickness. Many 













ART - !•] THEORY OF THE ARCH. 463 

arches in which the thickness is much less than one seventeenth 
of the span stand and carry heavy loads without showing any evi¬ 
dence of weakness. For example, in arch No. 26 of Table 63 (pp. 
502-3), which is frequently cited as being a model, the average thick¬ 
ness is 3.25 ft., or about one twenty-fifth of the span; and since no 
joints open, the line of resistance must lie in the middle third, 
e\en though the thickness is only one fifth of that required by the 
table. Owing to the approximations involved, and also to the limi¬ 
tations to arches having intrados and extrados parallel, the ordi¬ 
nary tables for the position of the joint of rupture have little, if 
an y> practical value. The only satisfactory way to find the angle 
of rupture is by trial by equation (5), as explained in § 681. 

According to M. Petit’s table, if the thickness is one fortieth of 
the diameter, the angle of rupture is 46° 12'; if the thickness is one 
twentieth, the angle is 53° 15'; and if one tenth, 59° 41'. 

In conclusion, notice that the investigations of both this and the 
preceding section show that an arch of more than about 90° to 120 Q 
central angle is impossible. 

683. Winkler’s Hypothesis. Prof. Winkler, of Berlin,—a well- 
known authority—published in 1879 in the “ Zeitsclirifi des Archi- 
tekten und Ingenieur Vereins zu Hannover ,” page 199, the follow¬ 
ing theorem concerning the position of the line of resistance: “For 
an arch ring of constant cross section that line of resistance is 
approximately the true one which lies nearest to the axis of the 
arch ring, as determined by the method of least squares.” * 

The only proof of this theorem is that by it certain conclusions 
can be drawn from the voussoir arch which harmonize with the 
accepted theory of solid elastic arches. The demonstration de¬ 
pends upon certain assumptions and approximations, as follows: 
1. It is assumed that the external forces acting on the arch are 
vertical; whereas in many cases, and perhaps in most, they are 
inclined. 2. The loads are assumed to be uniform over the entire 
span ; whereas in many cases the arch is subject to moving con¬ 
centrated loads, and sometimes the permanent load on one side of 
the arch is heavier than that on the other. 3. It is assumed that 
the load included between the lines PGD and NHC, Fig. 122 
(page 458), is equal in all respects to that included between PG'2 


* This theorem was first brought to the attention of American readers in 18S0, by 
Professor Swain in an article in Van Nostrand’s Engin’g Mag., vol. xxiii, pp. 265-76. 







164 


ARCHES. 


[CHAP. XVIII. 


and NHI. The error thus involved is inappreciable at the crown, 
but at the springingof semicircular arches is considerable. 4. The 
conclusions drawn from the voussoir (masonry) arch only approxi¬ 
mately agree with the theory of elastic (solid iron or wood) arches. 
5. Masonry arches do not ordinarily have a constant cross section 
as required by the above theorem; but it usually, and properly, 
increases toward the springing. 6. The phrase “ as determined by 
the method of least squares ” means that the true line of resist¬ 
ance is that for which the sum of the squares of the vertical 
deviations is a minimum. Since the joints must be nearly perpen¬ 
dicular to the line of resistance, the deviations should be measured 
normal to that line. For a uniform load over the entire arch, the 
lines of resistance are comparatively smooth curves; and hence, if 
the sum of the squares of the vertical deviations is a minimum, 
that of the normal also would probably be a minimum. But for 
eccentric or concentrated loads it is by no means certain that such a 
relation would exist. 7. The degree of approximation in this theorem 
is less the flatter the arch. 

684 . To apply Winkler’s theorem, it is necessary to (1) con¬ 
struct a line of resistance, (2) measure its deviations from the axis, 
and (3) compute the suin’of the squares of the deviations; and it is 
then necessary to do the same for all possible lines of resistances, 
the one for which the sum of the squares of the deviations is least 
being the “ true” one. 

Instead of applying Winkler’s theorem as above, many writers 
-employ the following principle, which it is asserted follows directly 
from that theorem: “ If any line of resistance can be constructed 
within the middle third of the arch ring, the true line of resistance 
lies within the same limits, and hence the arch is stable.” This 
assertion is disputed by Winkler himself, who says it is not, in gen¬ 
eral, correct.* It does not necessarily follow that because one line 
of resistance lies within the middle third of the arch ring, the 
“true” line of resistance also does; for the “true” line may coin¬ 
cide very closely with the axis in one part of the arch ring and 
depart considerably from it in another part, and still the sum of the 
squares of the deviations be a minimum. This method of applying 
Winkler’s theorem is practically nothing more or less than an appli- 

* Prof. Swain’s review of Winkler’s Theorem—Van Nostrand’s Engineering Maga¬ 
zine, vol. xxiii. p. 275. . 







ART. 1.] 


THEORY OF THE ARCH. 


465 


cation of the conclusions derived from the hypothesis of least 
resistance (§ 677). 

685. Navier’s Principle. It is well known, from the principles 
of fluid pressure, that the tangential thrust at any point of a circle 
pressed by normal forces is equal to the pressure per unit of area 
multiplied by the radius. “ The condition of an arch of any form 
at any point where the pressure is normal is similar to that of a cir¬ 
cular rib of the same curvature under a normal pressure of the same 
intensity ; and hence the following principle: the thrust at any 
normally pressed point of a linear arch is the product of the radius 
of curvature by the intensity of the pressure at that point. Or, 
denoting the radius of curvature by p, the normal pressure per 
unit of length of intrados by p, and the thrust by T, we have 

T=pp.” .(11) 


The above relation, due originally tolSTavier, has in itself nothing 
to do with the position of the line of resistance; but is employed by 
writers who assume that an arch is stable if a line of resistance can 
be drawn anywhere within the middle third of the arch ring, to 
determine the crown thrust. Notice, however, that under these 
conditions the radius of curvature is known only within limits. An 
example of its application will be referred to later (§ 704; and 8, 
§ 705;—pp. 482 and 486 respectively). 

686. Theories of the Arch. Various theories have been 
proposed from time to time, which differ greatly in the fundamental 
principles involved. Unfortunately, the underlying assumptions 
are not usually stated; and, as a rule, the theory is presented in such 
a way as to lead the reader to believe that each particular method 
«is free from any indeterminateness, and gives results easily and 
accurately . 99 Every theory of the masonry arch is approximate, 
owing to the uncertainty concerning the amount and distribution 
of the external forces (§ 666), to the indeterminateness of the posi¬ 
tion of the true line of resistance (§§ 676-85), to the neglect of the 
influence of the adhesion of the mortar and of the elasticity of the 
material, and to the lack of knowledge concerning the strength of 
masonry; and, further, the strains in a masonry arch are indeter¬ 
minate owing to the effect of variations in the mateiial of which the 




406 


ARCHES. 


[CHAP. XVIII. 


arcli is composed, to the effect of imperfect workmanship in dress- 
ing and bedding the stones, to the action of the center—its rigidity, 
the method and rapidity of striking it,—to the spreading of the 
abutments, and to the settling of the foundations. These elements 
are indeterminate, and can never be stated accurately or adequately 
in a mathematical formula ; and hence any theory can be at best 
ouly an approximation. The influence of a variation in any one of 
these factors can be approximated only by a clear comprehension of 
the relation which they severally bear to each other; and hence a 
thorough knowledge of theoretical methods is necessary for the 
intelligent design and construction of arches. 

A few of the most important theories will now be stated, and 
the fundamental principles involved in each explained. 

687 . To save repetition, it may be mentioned here, once for all, 
that every theory of the arch is but a method of verification. The 
first step is to assume the dimensions of the arch outright, or to 
make them agree with some existing arch or conform to some em¬ 
pirical formula. The second step is to test the assumed arch by the 
theory, and then if the line of resistance, as determined by the 
theory, does not lie within the prescribed limits—usually the middle 
third,—the depths of the voussoirs must be altered, and the design 
must be tested again. 

688. Rational Theory. The following method of determining 
the line of resistance is based upon the hypothesis of least crown 
thrust (§ 678), and recognizes the existence of the horizontal com¬ 
ponents of the external forces. Unfortunately, the results found 
by this method, as well as those by all others, are rendered some¬ 
what uncertain by the indeterminateness of the external forces 
(§ 666 ). 

689 . Symmetrical Load. General Solution. As an example 
of the application of this theory, let us investigate the stability of 
the semi-arch shown in Fig. 125 (page 467). The first step is to 
determine the line of resistance. The maximum crown thrust was 
computed in Table 59 (page 459), as already explained (§ 681). 
To construct the force diagram, a line BO is drawn to scale to 
represent the maximum thrust as found in the fourth line of the 
last column of Table 59. From 0, w 1 is laid off vertically upwards ; 
and from its extremity, h x is laid off horizontally to the left. Then 
the line from 0 to the left-hand extremity of h x (not shown in this 



ART. l.J 


46? 


RATIONAL THEORY OF THE ARCH. 


particular case) represents the direction and amount of the external 
force F l acting upon the first division of the arch stone ; and the 
line ifj from B to the upper extremity of represents the resultant 
pressure of the first arch stone upon the one next below it. Simi¬ 
larly, lay off w 2 vertically upwards from the left-hand extremity of 
h l9 and' lay off h a horizontally to the left; then a line F 2 from the 
upper end of w 2 to the left-hand end of h 2 represents the resultant 
of the external forces acting on the second divisions of the arch, 
and a line R 2 from the upper extremity of F 2 represents the resultant 
pressure of the second arch stone on the third. The force diagram 
is completed by drawing lines to represent the other values of 
tu 1 Ti x F x and the corresponding reactions. 



fn the diagram of the arch, the points in which the horizontal 
«nd vertical forces acting upon the several arch stones intersect, aie 
marked g x , g 2 , etc., respectively ; and the oblique line through each 
of these points shows the direction of the resultant external force 
acting on each arch stone. 

To construct the line of resistance, draw through U —the upper 



























468 


AKCHES. 


[CHAP. XVIII. 


limit of the middle third of the crown joint—a horizontal line to an 
intersection with the oblique force through g x ; and from this point 
draw a line parallel to R x , and prolong it to an intersection with the 
oblique force through . In a similar manner continue to the 
springing line. Then the intersection of the line parallel to R x 
with the first joint gives the center of pressure on that joint; and 
the intersection of R a with the second joint gives the center of 
pressure for that joint,—and so on for the other joints. Each 
center of pressure is marked by a circular dot. A line connecting 
these centers of pressure would be the line of resistance; but the 
line is not shown in Fig. 125. 

690 . The next step is to determine the degree of stability. 

1. Since the line of resistance lies within the middle third of the 
arch ring, and touches the inner limit of that third at two points 
and its outer limit at an intermediate and higher point, the factor 
against rotation is 3 (see § 669). 

2. The unit working pressure is found by applying equation (2), 


page 448. 


At the crown, d — \ and hence P = 


2 W 
l 


or, since 


W — 9,400 pounds and ^ = 1.25 feet, P = 15,040 pounds per square 
foot = 104 pounds per square inch. At the springing, W = 21,700 
pounds, l — 4.5 feet, and d — 0.10 feet; and therefore 


21,700 

4.5 


. 6 X 21,700 X 0.10 , _ _ 

H--= 4,820 -f- 643 = 5,463. 


That is, P = 5,463 pounds per square foot, or 38 pounds per square 
inch. Except for a particular kind of stone and a definite quality 
of masonry, it is impossible even to discuss the probable factor of 
safety; but it is certain that in this case the nominal factor is 
excessive (see § 223), while the real factor is still more so (see 
§§ 671-72). 

If the maximum pressure at the most compressed joint had been 
more than the safe bearing power of the masonry, it would have 
been necessary to increase the depth of the arch stones and repeat 
the entire process. Notice that the total pressure on the joints 
increases from the crown toward springing, and that hence the 
depth of the arch stones also should increase in the same direc¬ 
tion. 

3. To determine the degree of stability against sliding, notice 







ART. 1.] 


RATIONAL THEORY. 


469 


that the angle between the resultant pressure on any joint and 
the joint is least at the springing joint ; and hence the stability 
of this joint against sliding is less than that for any other. The 
nominal factor of safety is equal to the co-efficient of friction 
divided by tan (90° — 72°) = tan 18° = 0.33. An examination of 
Table 36 (page 315) shows that when the mortar is still wet the 
.eo-efficient is at least 0.50 ; and hence the nominal factor for the 
joint in question is at least 1and probably more, while the real 
factor is still greater. The nominal factor for joint 7 is at least 3^, 
and that for joint 3 is about 5. There is little or no probability that 
an arch will be found to be stable for rotation and crushing, and 
unstable for sliding. If such a condition should occur, the direc¬ 
tion of the assumed joint could be changed to give stability.* The 
actual joints should be as nearly perpendicular to the line of resist¬ 
ance as is consistent with simplicity of workmanship and with 
stability. For circular arches, it is ordinarily sufficient to make all 
the joints radial. In Fig. 125, the joints are radial to the intrados ; 
but if they had been made radial to the extrados or to an intermedi¬ 
ate curve, the stability against sliding, particularly at the springing 
joint, would have been a little greater. 

691 . Special Solution. The following entirely graphical solution 
is useful when it is desired to find a line of resistance which will 
pass through two predetermined points. 

For example, assume that it is desired to pass a line of resistance 
through U and a, Fig. 126 (page 470), the former being the upper 
extremity of the middle third of the crown joint and the latter the 
inner extremity of the middle third of joint 4. 

The value and positions of the external forces, which are the 
same as those employed in Fig. 125, are given in Table 59 (page 
459). Construct a load line, as shown in the force diagram, by 
laying oft w 1 and li x , and w 2 and A 2 , etc., in succession, and drawing 
F 9 P 2 , etc. Since the load is symmetrical, we may assume that the 
thrust at the crown is horizontal; and hence we may choose a pole 
at any point, say P', horizontally opposite O. Draw lines from P' 
to the extremities of F 1 , P 2 , etc. Construct a trial equilibrium 
polygon by drawing through U aline parallel to the line P'O, of 
the force diagram, and prolong it to b where it intersects F x . From 

* Strictly any change in the direction of the joints will necessitate a recomputation 
of the entire problem ; but, except in extreme cases, such revision is unnecessary. 





470 


AKCHES. 


[CHAP. XYIII. 


b draw a line b c parallel to R\ of the force diagram ; from c, the' 
point where be intersects the line of F 2 , draw a line c cl parallel to 
R\ ; from d, the point where c d intersects F % , draw a line d e 
parallel to R\; and from e, the point where d e intersects F A , draw 
a line e f parallel to R \. Prolong the line fe to g , the point in 



which it intersects the prolongation of U b ; and then, by the prin¬ 
ciples of graphical statics, g is a point on the resultant of the forces- 

F X> F *> and 

The section of the arch from the crown joint to joint 4 is at 
rest under the action of the crown thrust T, the resultant of the 
external forces, and the reaction of joint 4. Since the first two 
intersect at g, and since it has been assumed that the center of 
pressure for joint 4 is at a —the inner extremity of the middle third, 
—a line ctg must represent the direction of the resultant reaction of 
joint 4; and hence the line R A , in the force diagram drawn from 
the upper extremity of F A , parallel to a g, to an intersection with 
P'0, represents, to the scale of the load line, the amount of the 
reaction of joint 4. Then PO, to the same scale, represents the 
crown thrust corresponding to the line of resistance passing through 
U and a; and a line—not shown in Fig. 126—from the upper 




















ART. 1.] 


RATIONAL THEORY. 


471 


extremity of F 4 to the lower extremity of F x , would represent, in 
both direction and amount, the resultant of F lf F if F % , and F\ . 

Having found the thrust at the crown, complete the force dia¬ 
gram by drawing the lines R x , i? 2 , R 3 , etc. ; and then construct a 
new equilibrium polygon exactly as was described above for the 
trial equilibrium polygon. The construction may be continued to 
the springing line. The equilibrium polygon shown in Fig. 126 by 
a solid line was obtained in this way. 

The amount of the pressure on any joint is given by the length 
of the corresponding ray in the force diagram. The points in which 
the sides of tne equilibrium polygon cut the joints are the centers 
of pressure on the respective joints. The stability of the arch may 
be discussed as in § 690. 

692. One of the most useful applications of the method described 
in the preceding section is in determining the line of resistance for 
a segmental arch having a central angle so small as to make it 
obvious that the joint of rupture (§§ 680-81) is at the springing. 

For example, assume that it is required to draw the line of 
resistance for the circular arch shown in Fig. 127 (p. 472). The span 
is 50 feet, the rise 10 feet, the depth of voussoirs 2.5 feet, and the 
height of the earth above the summit of the arch ring is 10 feet. 
The angular distance of the springing from the crown is 43° 45'; 
and since the angle of rupture is nearly always more than 45°, it is 
safe to assume that the joint of rupture is at the springing. 

The method of determining the line of resistance is the same 
-as that explained in § 691, and is sufficiently apparent from an 
inspection of Fig. 127. 

693. TJnsymmetrical Load. The design for an arch ring 
should not be considered perfect until it is found that the criteria 
of safety (§§ 668-75) are satisfied for the dead load and also for 
every possible position of the live load. A direct determination of 
the line of resistance for an arch under an unsymmetrical load is 
impossible. To find the line of resistance for an arch under a 
symmetrical load, it was necessary to make some assumption com 
cerning (1) the amount of the thrust, (2) its point of application, 
aud (3) its direction ; but when the load is unsymmetrical, we 
neither know any of these items nor can make any reasonable 
hypothesis by which they can be determined. For an unsymmetri¬ 
cal load we know nothing concerning the position of the joint of 




472 


ARCHES. 


[CHAP. XVIII. 


rupture, and know that the thrust at the crown is neither horizontal 
nor applied at one third of the depth of that joint from the. 



crown ; and hence the preceding methods can not be employed. 
When the load is not symmetrical, the following method may be 
employed to find a line of resistance ; but it gives no indication as 
to which of the many possible lines of resistance is the true one. 

Let it be required to test the stability of a symmetrical arch hav¬ 
ing a uniform live load covering half the span. Divide the arch and 
its load into sections, as shown in Fig. 128. The live load is a ver¬ 
tical force, and the earth pressure would give a horizontal compo¬ 
nent. The approximate reduced-load contour for the vertical forces 
is shown in Fig. 128, and the horizontal and vertical components 
are laid off in the force diagram. An equilibrium polygon can be 
made to pass through any three points ; and therefore we may as¬ 
sume three points for a trial equilibrium polygon,—as, for example, 
(1) the lower limit of the middle third of the joint at the abutment 
Ay (2) the middle, C, of the crown joint, and (3) the upper limit 
of the middle third of the joint at B, 



























ART. 1.] 


RATIONAL THEORY. 


473 


Construct a force diagram by laying off: the external forces suc¬ 
cessively from 0 in the usual way (§ 689), selecting a pole, P', at any 
point, and drawing lines connecting P* with the points of division 
of the load line. Then, commencing at A, construct an equilib¬ 
rium polygon through A, C', and P', by the method explained in 
§§ 691-92. 

It is then necessary to move the pole of the force diagram in 
such a way that the equilibrium polygon will pass through B instead 
of B'. To do this, draw a line through the pole P', parallel to A B r 
—the closing line of the trial equilibrium polygon,—and then 
through H —the intersection of the preceding line with the load 
line—draw HP parallel to AB. The new pole, P, is at a point 



on this line such that HP IS to the horizontal distance from P' to 
the load line as C f D' is to CD. From P draw lines to the points 
of division of the load line, and then construct an equilibrium 
polygon through A, C, and B. If the resulting line of resistance 
does not lie within the middle third, try some other position of the 
three points A, C, and B instead of as above. If a line of resistance 
can not be drawn (see § 694) within the prescribed limits, then the 
section of the arch ring must be changed so as to include the line- 
of resistance within the limits. 

694. Criterion. If the line of resistance, when constructed by 
any of the preceding methods, does not lie within the middle third 
of the arch ring, the following process may be employed to deter¬ 
mine whether it is possible, or not, to draw a line of resistance in 
the middle third. 

Assume, for example, that the line of resistance of Fig. 129 lies 


i 
























474 


ARCHES. 


[CHAP. XVIII. 


outside of the middle third at a and b . Next draw a line of resist¬ 
ance through c and d, the points where 
normals from a and b intersect the outer 
and inner boundary of the middle third 
respectively. To pass a line of resistance 
through c and d, it is necessary to deter¬ 
mine the value and point of application of 
the corresponding crown thrust. The 
condition which makes the line of resist¬ 
ance pass through c is: the thrust multi¬ 
plied by the vertical distance of its point 
of application above c is equal to the load on the joint at c multi¬ 
plied by its horizontal distance from c. The condition that makes 
the line of resistance pass through d is: the thrust multiplied 
by the sum of the distance its point of application is above c and 
of the vertical distance between c and d is equal to the load on 
the joint at d multiplied by its horizontal distance from d. These 
conditions give two equations which contain two unknown quanti¬ 
ties—the thrust and the distance its point of application is above c . 
After solving these equations, the line of resistance can be drawn 
by any of the methods already explained. 

If this new line of resistance lies entirely within the prescribed 
limits, it is plain that it is possible to draw a line of resistance 
therein; but if the second line does not lie within the prescribed 
limits, it is not at all probable that a line of resistance can be drawn 
therein. The possibility of finding, by a third or subsequent trial, 
a line of resistance within the limits can not, in general, be answered 
definitely, since such a possibility depends upon the form of the 
section of the arch ring. 

If the line of resistance drawn through U and V goes outside of 
the arch ring beyond the extrados only, as at a , the second line of 
resistance should be drawn through c and V; and if, on the other 
hand, it goes outside below the intrados only, as at b , the second 
line should be drawn through U and d. 

695. Scheffler’s Theory.* This theory is the one most fre¬ 
quently employed. It is based upon the hypothesis of least crown 
thrust (§§ 678-82), and assumes that the external forces are vertical. 



* See the second foot-note page 455. 










ART. 1.] 


scheffler's THEORY. 


475 


This theory is frequently referred to as assuming that the arch 
stones are incompressible; but, fairly considered, such is not the 
case. Dr. Scheffler develops the theory of the position of the line 
of pressures for incompressible voussoirs; but subsequently states 
that the compressibility of the arch stones causes the line of resist¬ 
ance to retreat within the arch ring at points where it would other¬ 
wise reach the edge. He also says that, if a line of resistance can 
be drawn within the arch ring, that nowhere approaches nearer the 
edges of the joint than one fourth of its depth, the stability of the 
arch is assured. 

This theory will be illustrated by two examples. 

696. First Example. Assume that it is required to determine, 
in accordance with this theory, the line of resistance for the circular 
segmental arch shown in Fig. 130. The span is 50 feet, and the 



rise is 10 feet. The voussoirs are 2 feet 6 inches deep, and the 
spandrel wall rises 2 feet 10 inches above the summit of the arch 
ring. In this example we will follow the explanation used by 
Scheffler.* 

The first step is to find the amount and the point of application 
of the resultant of the external forces acting on the portion of the 
arch above the successive joints. Divide the semi-arch and the 
spandrel wall into any convenient number of parts by vertical lines 


* Cain’s “ Practical Theory of the Arch,” pp. 38-44. 




























4T6 


ARCHES. 


[CHAP. XVIII- 


through F, G, H, /, J, and K, as shown. The positions of the act¬ 
ual joints are assumed to be not yet fixed; but, for temporary pur¬ 
poses, assume radial joints to be drawn through F, G, H, /, J 7 
and K. Then the load on any part of the arch is assumed to be 
proportional to the area above it,—for example, the load on CHGR 
is assumed to be proportional to the area CNPD .* 

Having determined the area representing the loads, it is then 
necessary to determine (1) the numerical values of the several loads 
and the distances of their centers of gravity from a vertical through 
the crown, and (2) the amount and the position of the center of 
gravity of the loads above any joint. The steps necessary for this 
are given in Table GO. 

The quantities in column 2 of Table 60 are the lengths of the- 
medial lines of the several trapezoids. Column 6 contains the 

* Notice that really the load on the joint SR, for example, is SRNPGll, and not 
CNPD as above. The error is least near the crown of flat segmental arches, and 
greatest near the springing of semi-circular ones. The error could be eliminated (1) 
by finding the weights of GPNH and RGHS separately and combining them into 
a single resultant for the weight on the joint SR, as was done in §681; or (2) by 
drawing the arch to a large scale on thick paper and cutting out the several six-sided 
figures which represent the loads, when the amounts of the several loads can be 
determined readily from the weights of corresponding sections of the paper, and the 
center of gravity of each section can be found by balancing it on a knife edge. 

Scheffler gives the following empirical and approximate method of altering the 
position of the joints to correct this error. Let BCG, Fig. 131, be the side of the 
trapezoid, and CR the uncorrected joint. From b, the middle point of GR, draw 



bB ; and draw Gc parallel to bD, and ch parallel to CR. Then will ch be the correct ed 
joint. Conversely, having given the joint CR, Fig. 132, to find the side of the trape¬ 
zoid which limits the portion of the load upon it, through Cdraw DG vertical and 
draw Cg parallel to Bb (b being the middle point of GR) ; then, from g, draw dg ver¬ 
tical, and we have the desired side of the trapezoid. 












£RT. 1.] 


SCHEFFLEE^S THEOEY. 


477 


TABLE 60. 

Application op Scheffler’s Theory to the Arch Ring shown in 

Fig. 130, page 475. 


1 

o 

td 

3 

4 

5 

c 

The Amount, and 

Position 

OF THE 

►— 1 

Center of Gravity, of 

THE 

o* 


Several Loads. 


55 O 

oo • 









t-l 'Z. 

£ z 2 

p Pio 

Dimensions of the sections. 

<£) 

g *5 g 

<8 U O 

to ^0*3 

S W H 







c3 ~ 





•*-> 0> r* . • 

o , S 




ogS 

H O 

c ® 03 

Height. 

Width. 

Area. 

.s § ® a 

s- O 





O C4-( CI_I s' 

O Ocw 

1 

5.4 

5 

27.0 

2.5 

2 

6.1 

5 

30.5 

7.5 

3 

7.6 

5 

38.0 

12.5 

4 

9.8 

5 

49.0 

17.5 

5 

13.2 

5 

66.0 

22.5 

6 

14.5 

1.75 

25.4 

25.9 


6 

7 

8 

9 

TO FIND 

the Amount, and the Center 

of Gravity, of 

the Loads above 


the Several Joints. 


o 

<D 


CO 

<d a © 

© <V X} . 

CO 


8 w-*2 

fl Oaj^ to 

oment of each 
ion about U. 

rea of the load 
.bove the succe 

ive joints. 

oments of the 1< 

.bove the succe 

ive joints, aboi 

orizontal dista 

rom U to the 

er of gravity o 

he loads above 

uccessive joint 



g W Cfi 

pH <*-H +-> -*H> CO 

67.50 

27.0 

67.50 

2.5 

228.75 

57.5 

296 25 

5.1 

475.00 

95.5 

771.25 

8.1 

857.50 

144.5 

1,628.75 

11.3 

1,485.00 

210.5 

3,113.75 

14.7 

657.86 

235.9 

3,771.61 

16.0 


products of the numbers in columns 4 and 5. Column 7 contains 
the continued sums of the quantities in column 4. Column 8 con¬ 
tains the continued sums of the quantities in column 6. Column 9 
is found by the principle of analytical mechanics : the distance 
of the center of parallel forces from any point is equal to the sum 
of the moments of the several forces about that point divided by 
the sum of the several forces; and hence the numbers in column 
9 are found by dividing the quantities in column 8 by the corre¬ 
sponding quantity in column 7. 

697. The second step is to find the minimum thrust which 
applied at U (UF = FE) is sufficient to prevent the semi-arch 
from rotating. The origin of moments is considered as being in 
the successive joints at one third of the depth of each from the 
intrados. 

If T= the thrust and y = its arms, and W — the load above 
any joint and x = its arm, then for equilibrium about any joint 



(12) 


It is required to find the maximum value of T. 











































478 


ARCHES. 


[CHAP. XYIII. 


The W -—in terms of the weight of a cubic foot of the masonry—■ 
for each joint is the corresponding number in column 7 of Table 60, 
and is for convenience repeated in column 2 of the table below. The 
x for each joint is the horizontal distance between the resultant of 
the load above each joint and the center of moments for that joint; 
and is equal to the horizontal distance from U to the points 1, 2, 
etc., minus the respective quantities in column 9 of Table GO. 
The first of these quantities is given in column 3 of Table 61, the 
second in column 4, and their difference in column 5. The y for 
each joint is given in column 6 of Table 61. The value of the 
thrust, obtained by substituting the above data successively in equa¬ 
tion (1.2) and solving, is given in column 7 of Table 61. 

TABLE 61. 

Application op Scheffler’s Theory to the Arch Ring shown in 

Fig. 130, page 475. 


1 

2 ' 

3 

4 

5 

6 

7 

No. of the Joint, 

COUNTING FROM 
THE ONE NEXT TO 

the Crown. 

Area of the load 
above each joint 
(= W). 

Horizontal dis¬ 
tance from U to 

1, 2, 3, etc., re¬ 
spectively. 

Horizontal dis¬ 
tance from U to 
the center of 
gravity of the 
loads above the 
successive joints. 

Arm of the load 
about the center 
of resistance of 
the successive 
joints (= x). 

Arm of the thrust 
about the center 
of resistance of 
each joint ( = y) 

Horizontal thrust 
required to pre¬ 
vent rotation 
about the suc¬ 
cessive joints 
( = T). 


1 

27.0 

4.8 

2.5 

2.3 

1.15 

54.0 


2 

57.5 

9.6 

5.1 

4.5 

2.09 

123.6 


3 

95.5 

14.4 

8.1 

6.3 

3.72 

116.9 


4 

144.5 

19.2 

11.3 

7.9 

6.16 

185.3 


5 

210.5 

24.0 

14.7 

9.3 

9.60 

204.0 


6 

235.9 

25.6 

16.0 

9.6 

11.00 

205.9 


The horizontal thrust for joint 6 is the greatest, and hence that 
joint is the joint of rupture. This result might have been antici¬ 
pated, since the angle of rupture ordinarily varies between 45° 
and 60° (see last paragraph of § 682, page 463), while the angular 
distance of joint 6 from the crown is only 43° 35'. 

698. The second step is to construct the line of resistance. 

To find the center of pressure on joint 1, Fig. 130, page 475, draw 
a horizontal line through U , and lay off, to any convenient scale, a 
distance Ua to the left equal to the first quantity in column 4 of 
Table 61. a is a point through which the weight of DEQP* 


* Assumed to be equal to HEQPG (see foot-note, page 476). 



























ART. 1.] 


SCIIEFFLER^S THEORY. 


479 


acts. Lay off, vertically, a distance ab equal to the first quantity 
in column 2 of Table 61; this line represents the weight of the first 
voussoir and the load resting upon it. From b lay off, horizontally 
to the right, a distance be equal to the last quantity in column 7 of 
Table 61. This line represents the horizontal pressure at the crown. 
Then, by the principle of the triangle of forces, a line ca repre¬ 
sents the resultant pressure on the joint EG; and this line pro¬ 
longed intersects the joint EG at d } which is, therefore, the center 
of pressure on that joint. 

To find the center of pressure on the second joint, lay off from 
U, horizontally to the left, a distance equal to the second quantity 
in column 4 of Table 61; erect a vertical equal to the second quan¬ 
tity in column 2; and from the point thus found lay off, horizon¬ 
tally to the right, a quantity equal to the last quantity in column 7. 
Then draw the third side of the triangle of forces, and prolong it 
until it intersects the joint at e. 

By a similar construction, the centers of pressure for the several 
joints are determined to be U, d , e,f, g, h, and 6, as shown in Fig. 
130. A line joining these points is the line of resistance (not shown 
in the figure). 

699. The preceding method of drawing the line of resistance 
has two advantages: (1) The center of pressure on any joint may 
be found at once; and (2) any small error in draughting is confined 
to the joint where it first occurs. Notice, however, that the method 
is applicable only when the horizontal component of the pressure on 
the several joints is constant; that is, this method is applicable only 
when the external forces are assumed to be vertical. 

Having determined the line of resistance by the above method, 
the stability of the arch can be discussed as described in § 690. 

700. Second Example. Let us construct, according to this 
theory, the line of resistance for the semi-arch shown in Fig. 133, 
page 480, which is the same one discussed in § 681, where it was 
shown that joint 4 is the joint of rupture, and that, if the horizon¬ 
tal forces be disregarded, the maximum crown thrust is 8,748 
pounds (see Table 59, page 459). 

The crown thrust is laid off, to any convenient scale, from 8 
to O ; and the loads as given in Table 59 are laid off, to the same 
scale, successively from O downwards. The remainder of the 




480 


ARCHES. 


[CHAP. XYIII. 


construction—shown by dash lines—is exactly similar to that 
described in § 689 in connection with Fig. 125, page 467. 



701. Erroneous Application. Frequently the principle of the 
joint of rupture is entirely and improperly neglected in applying 
this theory; that is to say, the crown thrust employed in determin- 






























ART. 1.] 


SCHEFFLER ? S THEORY. 


481 


ing the line of resistance is that which would produce equilibrium 
of rotation about the springing line, instead of that which would 
produce equilibrium about the joint of rupture. For example, 

instead of employing the maximum value in the - column of 

V 

Table 59, page 459, the last quantity in that column is used. 

The line of resistance obtained by this method is shown in Fig. 
133 (page 480) by the dotted line, the crown thrust (5,990, as com¬ 
puted in Table 59, page 459) being laid off: from G to 0, to the scale 
employed in laying off the load line. 

702. The error of this method is shown, incidentally, in §§ 678- 
82 and §§ 688-701, and needs no further explanation. 

The amount of the error is illustrated in Fig. 133. According 
to this analysis, the line of resistance is tangent to the intrados, 
which seems to show that the arch can not stand for a moment. 
However, many such arches do stand, and carry a heavy railroad 
traffic without any signs of weakness ; and further, any reasonable 
method of analysis.shows that the arch is not only safe, but even 
-extravagantly so (§ 690). 

This method of analysis certainly accounts for some, and per¬ 
haps many, of the excessively heavy arches built in the past. For 
example, compare 8 and 9, 17 and 18, 33 and 34, 52 and 54, etc., 
of Table 63 (page 502). 

703. Reliability of Scheffer's Theory. For the sake of com¬ 
parisons, the line of resistance according to the Rational Theory 
(§§ 688-94), as determined in Fig. 125 (page 467), is shown in Fig. 
133 by the solid lines. (Notice that Fig. 133 gives the lines of re¬ 
sistance, and not the equilibrium polygons as in Fig. 125.) In this 
particular case, the difference between the two lines above the joint 
of rupture is not material ; but the difference below that joint has 
a very important effect upon the thickness of the arch at the spring¬ 
ing, and also upon the thickness of the abutment (§ 712). 

If the maximum ratio of the horizontal to the vertical compo¬ 
nent of the external forces (see first paragraph on page 460) had 
been employed in determining the crow T n thrust and the line of 
resistance, there would have been a material difference in the posi¬ 
tion of both the joint of rupture and the line of resistance above 
that joint. Although the horizontal components of the external 
forces can not be accurately determined, any theory that disregards 





482 


ARCHES. 


[CHAP. XVIII. 


the existence of these forces can not be considered more than a 
loose ajDproximatiou. 

704. Rankine’s Theory. Although this theory has long been 
before the public and is in some respects much superior to the one 
in common use, it is comparatively but little employed in practice. 
This is probably due, in part at least, to the fact that Rankine’s 
discussion of the theory of the masonry arch is not very simple nor 
very clearly stated, besides being distributed throughout various 
parts of his works.* 

Rankine determines the thrust at the crown by Navier’s princi¬ 
ple (§ 685); but he makes no special assumption as to the point of 
application of this thrust, further than to assume that if a line of 
resistance can be drawn anywhere within the middle third of the 
arch ring, the arch is stable. 

In that part of his books which precedes the discussion of arches, 
Rankine investigates the various curves which a cord will assume 
under different distributions of the load ; and subsequently adopts 
these curves as the form which the line of resistance of an arch 
similarly loaded should have. The discussion of these curves con¬ 
stitutes the most valuable part of his investigations concerning the 
stability of the masonry arch. 

705. Curvature of the Linear Arch. The curves assumed by 
a cord under the various conditions of loading, can be applied to 
linear arches (the line of resistance of actual arches) by imagining 
that the curve of the cord is reversed, and that the cord itself is 
replaced by a thin metal strip, which, like the cord, shall be prac¬ 
tically without transverse strength, but which, unlike the cord, 
shall be able at every point to resist a compressive, force in the di¬ 
rection of its length. The amount and distribution of the external 
forces are the same in both cases ; but with the cord they act out¬ 
ward, while with the linear arch they act inward. The formulas 
and diagrams are essentially the same in both cases. The curves 
assumed by a suspended cord under various distributions of the 
load will now be briefly considered. In each case it will be assumed 
that the ends of the suspended cord and also of the corresponding 
linear arch are in the same horizontal line. 

I. If the cord is acted upon by vertical loads distributed uni- 


* “Civil Engineering,” and “ Applied Mechanics.’’ 





ART. 1.] 


rahkihe’s THEORY. 


483' 


formly along the horizontal, it will assume the form of a parabola . 
This case does not occur with masonry arches. 

2. If the load is vertical and distributed uniformly along the 
curve, the resulting curve is the common catenary, of which the 
equation is 

m t — _ *\ 

y- j\ Em + E ra j’ 



in which y is the ordinate to any point, m the ordinate to the apex, 
E the base of the Naperian logarithms, and x the abscissa corre¬ 
sponding to y. Approximately, this case may occur with masonry 
arches, since the above law of loading is nearly that of an arch 
whose intrados is the common catenary and which supports a span¬ 
drel wall of masonry having a horizontal upper surface (see 2, page 
445). 

3. Three points fix the common catenary ; and hence, if the posi¬ 
tion of the springing lines and the crown are assumed, the depth off 
the load at the crown is fixed by the equation of the curve. This 
limitation would often interfere with the use of the common cate¬ 
nary in building arches. To meet this difficulty, Rankine trans¬ 
forms the common catenary by the principle of what he calls paral¬ 
lel projections, i. e., by increasing or decreasing one set of the 
rectangular co-ordinates to the curve without changing the other, 
and obtains the transformed catenary. The equation of the 
curve is 

y = h\ E % + E~™\, .(14) 


in which y 0 is the ordinate to the apex, and m is the modulus of the 
curve and is found by the formula 


hyp- lo s- (•“ + 

The determination of values of y by equation (14) is not easy except 
with either a table of Naperian logarithms or a table of results 
deduced therefrom, and even then it is tedious. 

With this curve we may assume the springing lines, the crown, 
and the depth of load at the crown, and then compute the curve of 
equilibrium. The transformed catenary differs from a circular arc 
between the same points only in being slightly (and frequently only 







484 


ARCHES. 


[CHAP. XVIII. 


very slightly) sharper in the haunches ; and hence it is not neces¬ 
sary to discuss it further.* 

4. If the load is uniform and normal at every point, the curve 
of equilibrium is plainly a circle . An example of this case would be 
an empty masonry shaft standing in water. 

5. The ellipse is the form assumed by a cord under a load com¬ 
posed of horizontal and vertical components which are constant 
along the horizontal and vertical lines, but which differ from each 
other in intensity. There is no case in ordinary practice where the 
pressures upon an arch are strictly identical with those which give 
an elliptical curve of equilibrium. The curve of equilibrium of a 
tunnel arch through earth, when the depth below the surface is 
great compared with the rise of the arch itself, approximates to an 
ellipse. The load is nearly uniform along the horizontal, while the 
horizontal force at any point is some fractional part of the vertical 
one at the same point; and therefore the horizontal forces are 
nearly uniform. It is readily shown that the intensity (the pressure 
per unit of area perpendicular to the force) of the vertical com¬ 
ponent is to that of the horizontal component as the square of the 
vertical diameter of the ellipse is to the square of its horizontal 
diameter; f that is to say, 

the horizontal axis _ . /intensity of horizontal component 
the vertical axis intensity of vertical component * ' 

6. If the forces acting on the linear arch are normal and 
increase in intensity in proportion to the distance of the points of 
application from a horizontal line, the curve is a hydrostatic arch. 
A tunnel under water is an example of this method of loading. 
The form of the curve is shown in Fig. 134, of which only the portion 

BA C is available in the construction of 
arches. The equation of the curve is 

p P = wpo Po = a constant , . (17) 

in which p is the normal pressure on a 
unit area at any point, p the radius of 

* For two numerical examples of the method of employing the transformed cate¬ 
nary in the design of an arch, see an article by W. H. Booth in Van Nostrand’s 
Engin’g Mag., vol. xxxi, pp. 1-10; and for another, see an editorial in Engineering 
News , vol. xviii, p. 372. 

t Rankine’s Civil Engineering, p. 205. 










ART. 1.] 


rankine’s THEORY. 


485 


•curvature at the same point, y the distance from the line 0 (the 
■surface) to any point, p 0 and y 0 the values of p and y for the point 
A, and w the weight of a unit of volume of the loading. 

“ The true semi-ellipse of a given span and rise differs from the 
hydrostatic arch by being of somewhat sharper curvature at the 
“Crown and springing and of somewhat flatter curvature at the 
haunches, and by enclosing a somewhat less area. The application 
of the hydrostatic arch to practice is founded on the fact that every 
arch, after having been built, subsides at the crown, and spreads, 
or tends to spread, at the haunches, which therefore press horizon¬ 
tally against the filling of the spandrels ; from which it is inferred 
as probable that, if an arch be built of a figure suited to equilibrium 
under fluid pressure— i. e ., pressure of equal intensity in all direc¬ 
tions,—it will spread horizontally, and compress the masonry of the 
spandrels until the horizontal pressure at each point becomes of 
■equal intensity to the vertical pressure, and is therefore sufficient to 
keep the arch in equilibrio.” * 

7. If the vertical and the horizontal components of the normal 
force differ from each other but both vary as the distance of the 
point of application from a horizontal line, the curve of equilbrium 
is the gcostatic arch. An arch in clean dry sand is the best example 
of this form of loading. The geostatic arch bears the same relation 
to the hydrostatic arch that the ellipse does to the circle. The 
geostatic curve can be produced from that of the hydrostatic curve 
by increasing or decreasing one set of ordinates without altering the 
other. If p x be the horizontal intensity of the forces acting on the 
hydrostatic arch and p' x be that for the geostatic arch, then 
p x = cp' x ; and if x is the horizontal diameter at any point of 
the hydrostatic curve and x f the same for the geostatic, then 
X* — C X. f 

8. Rankine next discusses the following more general problem : 
<e Given the curve of a linear arch and the vertical components of a 
symmetrical load, to find the intensity and distribution of the 
horizontal components necessary to produce equilibrium. 


* Rankine’s Civil Engineering, pp. 419-30. 

f For a numerical example of the method of employing the geostatic curve for the 
intrados of tunnel arches, see an article—“ The Employment of Mathematical Curves 
as the Intrados of Arches by W. H. Booth in Van Nostrand’s Engin’g Mag., vol. 
xxx, pp. 355-60. 





486 


ARCHES. 


[chap, xvnr. 


“ Let V = the vertical load on any arc DC, —represented in 
Fig. 135 by the line EG', 

V x — the vertical load on the semi-arch A C\ 

H — the horizontal load on any arc DC, —represented by 
the line GF, Fig. 135 ; 

H x — the horizontal load on the semi-arch A C; 

H 0 = the compression at the crown C, —represented by the 
line EC, Fig. 135; 

C = the compression on the rib at any point D ,—repre¬ 
sented by ED, Fig. 135 ; 

p x = the intensity of the horizontal force, i. e., the force 
per unit of area perpendicular to its line of action* 
p v = the intensity of the vertical force; 
p 0 = the value of p y at the crown C; 
p 0 = the radius of curvature at the crown C; 
i = the angle that the tangent of the linear arch at any 
point makes with the horizontal,—that is, i = the- 
angle EDG, Fig. 135. 



C — V cosec i; .. . . 

H — V cot i; . 

_ dH_ _ _ d (Foot i) _ _ d ( F rfy) 
Px ~ dy ~ dy ~ dy 


(19) 

( 20 ) 

( 21 ) 


The integration constant for (21) is H 0 ; and is found by equa¬ 
tion (11), page 465, which, in the above nomenclature, becomes 


H, — po Po 














ART. 1.] 


RANKIXE'S THEORY. 


487 


However, before concluding this phase of the discussion of 
arches, it is well to state that the only arches in common use are 
the circular either semi-circular or segmental—and the elliptic. 

706. Stability of any Proposed Arch. To apply the preceding 
principles in designing an arch, it is necessary to know both the 
vertical and the horizontal forces acting on the arch. Rankine 
assumes* (1) that the vertical force acting on any part is the weight 
of the masonry, earth, or other load vertically above the same; and 
(2) that the horizontal pressure of earth is given by the formula 


p x = w d 


1 — sin 0 f 
1 4- sin 0 ? 


• ( 23 ) 


in which p x is the horizontal intensity at any point, w the weight of 
a unit of the earth, d the depth of earth over the point, and 0 the 
angle of repose. In the above nomenclature, the vertical inten¬ 
sity is 

Vv=wd .(24) 


By an application of these two principles are to be determined the 
amount and distribution of the vertical and the horizontal forces 
acting on the arch; and then the equilibrium curve corresponding 
to this form of loading (see § 705) is to be adopted for the intrados 
of the proposed arch. 

For an example, take the case of an arch under a high bank of 
earth whose angle of repose is 30°. Strictly, the curve of equi¬ 
librium is the geostatic arch (see paragraph 7, § 705); but it will 
be more simple and sufficiently exact, if we assume it to be an 
ellipse, which is equivalent to assuming that the rise of the arch is 
inconsiderable in comparison with the depth of earth over it. The 
intrados is then to be an ellipse in which 


the vertical axis 
the horizontal axis 




“ If the earth is firm, and little liable to be disturbed, the propor¬ 
tion of the half-span—or horizontal semi-axis—to the rise—or ver- 


* Civil Engineering, p. 434. 

t Rankine states (Civil Engineering, p. 320) that the horizontal pressure can not 
be greater than w nor ^ ess than w Notice that the value employed 


1—sin<£ 

above is the minimum. 

















488 


ARCHES. 


[CHAP. XVIII. 


tical semi-axis—may be made greater than is given by the preced¬ 
ing equation, and the earth will still resist the additional horizontal 
thrust; but that jiroportion should never be made less than the- 
value given by the equation, or the sides of the archway will be in 
danger of being forced inwards.” * 

“ There are numerous cases in which the form of the linear rib 
suited to sustain a given load may at once be adopted for the in- 
trados of a real arch for sustaining the same load, with sufficient 

exactness for practical purposes. The follow- 
j a ing is the test whether this method is appli¬ 
cable in any given case. Let A CB in Fig. 
136 be one half of the ideal rib which it is- 
proposed to adopt as the intrados of a real 
arch. Draw A a normal to the rib at the 
crown, so as to represent a length not ex¬ 
ceeding two thirds of the intended depth of 
Draw a normal Bb at the springing of a length 



Fig. 136, 

the keystone, 
such that 


Bb _ thrust along rib at A „ 
A a ~ thrust along rib at B ‘ 


t 


( 26 > 


The thrust at A is found by equation (11), page 465 ; and the thrust 
at any other point is given by equation (19), page 486. Construct 
a line acb such that its perpendicular distance from the intrados at 
any point, cC, is inversely as the thrust along the rib at that point. 
Then if acb lies within the middle third of the proposed arch ring, 
the ideal rib ACB is of a suitable form for the intrados. 

707. Rankine’s general method of determining the stability of 
a proposed arch is as follows: \ 

“The first step towards determining whether a proposed arch 
will be stable, is to assume a linear arch parallel to the intrados or 
soffit of the proposed arch, and loaded vertically with the same 
weight, distributed in the same manner. Then by equation (21), 
page 486, determine either a general expression, or a series of val¬ 
ues, of the intensity p x of the conjugate pressure, horizontal or 
oblique as the case may be, required to keep the arch in equilibria 


* Rankine’s Civil Engineering, p. 434. 
t Ibid., p. 417. 

X Ibid., pp. 421-22. 










ART. 1.] RANKINE’S THEORY. 489' 

under the given vertical load. If that pressure is nowhere nega¬ 
tive, a curve, similar to the assumed arch, drawn through the middle 
of the arch ring will be, either exactly or very nearly, the line of 
pressure of the proposed arch; p x will represent, either exactly or 
very nearly, the intensity of the lateral pressure which the real 
arch, tending to spread outwards under its load, will exert at each 
point against its spandrel and abutments; and the thrust along the 
linear arch at each point will be the thrust of the real arch at the 
corresponding joint. 

“ On the other hand, if p x has some negative values for the 
assumed linear arch, there must he a pair of points in that arch 
where that quantity changes from positive to negative, and is equal 
to nothing. The angle of inclination i at that point, called the 
angle of rupture,is to be determined hyplacing the second member 
of equation (21), page 486, equal to zero and solving for cot i. The 
corresponding joints in the real arch are called the joints of rup¬ 
ture ; and it is below those joints that conjugate pressure* from 
without is required to sustain the arch and that consequently the 
hacking must be built with squared side-joints. 

“In Fig. 137, let BCA represent one half of a symmetrica.’ 
arch, KLDE an abutment, and C 
the joint of rupture—found by the 
method already described. The point 
of rupture, which is the center of re¬ 
sistance of the joint of rupture, is 
somewhere within the middle third 
of the depth of that joint; and from 
that point down to the springing joint 
B, the line of pressure is a curve sim¬ 
ilar to the assumed linear arch, and E l JD 
parallel to the intrados, being kept in . FlG - 137 - 

equilibrio by the lateral pressure between the arch, and its spandrel 
and abutment. 

“ From the joint of rupture C to the crown A, the figure of the 
true line of pressure is determined by the condition that it shall be 

* A minus value of p x will correspond to an outward pull, and consequently the 
backing below the joint of rupture should be capable of resisting tension. 














490 


ARCHES. 


[CHAP. XVIII. 


a linear arch balanced under vertical forces only ; * that is to say, 
the horizontal component of the thrust along it at each point is a 
constant quantity, and equal to the horizontal component of the 
thrust along the arch at the joint of rupture. 

“ The only point in the line of pressure above the joint of 
rupture which it is important to determine is that of the crown of 
the arch, A) and it is found in the following manner : Find the 
center of gravity of the load between the joint of rupture C and the 
crown A; and draw through that center of gravity a vertical line. 
Then if it be possible, from any point, such as M, in that vertical 
line, to draw a pair of lines, one parallel to a tangent to the soffit at 
the joint of rupture and the other parallel to a tangent to the soffit 
at the crown, so that the former of those lines shall cut the joint of 
rupture and the latter the keystone, in a pair of points which are 
both within the middle third of the depth of the arch ring, the 
stability of the arch will be secure ; and if the first point be the 
point of rupture, the second will be the center of resistance at 
the crown of the arch and the crown of the true line of pressures. 

“ When the pair of points, related to each other as above, do not 
fall at opposite limits of the middle third of the arch ring, their 
exact positions are to a small extent uncertain ; but that uncertainty 
is of no consequence in practice. Their most probable positions are 
equidistant from the middle line of the arch riug. 

“ Should the pair of points fall beyond the middle third of the 
arch ring, the depth of the arch stones must be increased/’ 

708. Reliability of Rankine’s Theory. 1. This theory is ap¬ 
proximate since it makes no attempt to determine the true line of 
resistance, but finds only a line of resistance which lies within the 
middle third of the arch ring. 

2. The value of the radius of curvature to be used in finding 
the crown thrust is indeterminate. It is frequently, but erroneously, 
taken as the radius of the intrados at the crown. 

3. The method of finding the center of pressure at the crown 
and also at the joint of rupture assumes that the portion CM A, 
Fig. 137, is acted upon by only three forces ; viz., the vertical load, 
the thrust at the crown, and the pressure on the joint of rupture. 

* From this it appears that Rankine himself disregards, for that part of the arch 
above the joint of rupture, the principal characteristic of his theory, viz.: the recog* 
nition of the horizontal components of the external forces; and hence this theory 
is, in fact, the same as Scheffler’s (§§ 695-703). 







ART. 1.] 


RANKINE^S THEORY. 


491 


This is erroneous («) because it neglects the horizontal components 
of the external forces, and hence the actual center of pressure at 
the joint of rupture is nearer the intrados than the position of C 
as found in Fig. 137 ; and (b) because it finds a new value for the 
thrust at the crown which, in general, will differ from that employed 
in finding the position of the joint of rupture. 

4. Rankine himself says that the method of § 707 is inapplicable 
to a circular arch greater than 90°, and gives a complicated formula 
for that case. 

Rankine’s theory is more complicated and less accurate than 
either Scheffier’s (§ 695) or the rational theory (§ 688). 

709. Other Theories of the Arch. There are several methods, 
in more or less common use, of determining the stability of the vous- 
soir arch, many of which are but different combinations of the pre¬ 
ceding principles, while some have a much less satisfactory basis. 
It is not necessary to discuss any of these at length; but there is 
one which, owing to the frequency with which it is employed, 
requires a few words. It is the same as Scheffler’s (§§ 695-703), ex¬ 
cept in assuming that the line of resistance passes through the 
middle of the crown joint and also through the middle of the spring¬ 
ing joint. The line of resistance is then determined in any one of 
a number of ways ; and the arch is said to be stable, if the line of 
resistance lies in the middle third of the section of the arch ring. 
This theory is much less satisfactory than ScheffleFs and possesses 
no advantage over it. 

710. Theory OF the Elastic arch. It has long been recognized 

that all theories for the voussoir arch are very unsatisfactory ; and 
hence it has been proposed to consider the masonry arch as an 
elastic curved beam fixed at its ends, and examine'its stability by 
the principles employed in computing the strains in arches of iron 
or wood. There is no essential difference, as far as the theory is 
concerned, between the iron and the stone arch ; but there is great 
difficulty in applying the mathematical theory of elasticity to the 
masonry arch. The theory of elasticity when applied to the 
masonry arch has the following sources of error, in addition to those 
of the ordinary theory of the elastic arch : 1. There is great un¬ 
certainty as to the external forces (§ 666). 2. We have no definite 

knowledge concerning either the modulus of elasticity (§§ 16 and 
146) or the ultimate strength of masonry (§§ 221-23, and §§ 246- 



492 


ARCHES. 


[chap, xviir. 


49). 3. The stone arch is not homogeneous ; i. e ., the modulus of 

elasticity is not constant, but varies between that of the stone and 
the mortar. 4. Slight imperfections in the workmanship—as, for 
example, a projection on the bearing surface of an arch stone or a 
pebble in the mortar—would break the continuity of the arch, and 
render the theory inapplicable. 5. The stability of the arch would 
be greatly influenced by the action of the center,—its rigidity, the 
method of loading it to prevent deformation, and the method and 
rapidity of striking it. 

The application of the theory of elasticity to stone arches has 
been considerably discussed in late years ; but it is generally con¬ 
ceded that the results are, for the most part, illusory, since the 
much simpler methods give results equally reliable. The explana¬ 
tion of the theory of the elastic masonry arch as given by Professor 
Greene in Part III—Arches—of his “Trusses and Arches” is all 
that can be desired; and hence this theory will not be discussed 
here. 

711. Stability of Abutments and Piers. The stability of the 
abutment is in a measure indeterminate, since it depends upon the 
position of the line of resistance of the arch. The stability of 
the abutment may be determined most easily by treating it as a 

part of the arch, i. e., by extending the 
load line so as to include the forces acting 
upon it and drawing the reactions in the 
usual way ; or its stability may be deter¬ 
mined as follows : Assume that it is re¬ 
quired to test the stability of the abutment 
shown in Fig. 138. Let qc represent the 
direction of the resultant pressure on the 
joint AB. g is the center of gravity of the 
section ABC of the abutment, and g 2 that 
for the section ABED A At a —the point 
fig. i3s. where a vertical through g intersects qc x 

prolonged—lay off, to scale, a line ad equal to the weight of ABC, 
and also a line ab equal to the pressure qc x ; then c 2 —the point 
where the diagonal ea pierces A C —is the center of pressure on A C. 



* For a method of finding the center of gravity when the section is a trapezoid, 
see the third paragraph of § 494 (page 318). 







k RT * !•] STABILITY OF THE ABUTMENT. 493 

In a similar manner, c 3 is found to be the center of pressure on 
EE. 

The amount of the pressure on A C is given by the length of the 
line ae ; and the stability of the joint against crushing can be de¬ 
termined as described in §§ 670-72 and paragraph 2 of § 690. 
The stability*against rotation may be determined as described in 
§ 669 and paragraph 1 of § 690. A line—not shown—connecting 
c i> c 2 > C 3 > is the line of resistance of the abutment, to which the 
joints should be nearly perpendicular (see § 674 and division 3 of 
§ 690). 

712. In Fig. 133 (page 480) is shown the line of resistance for 
the abutment according to the rational theory of the arch (§§ 688- 
94), and also that according to ScheffleFs theory (§§ 695-703),— 
the former by the solid line and the latter by the broken one. 
Since to overestimate the horizontal components of the external 
forces would be to err on the side of danger, in applying the former 
theory in Fig. 133, the horizontal component acting against the 
abutment was disregarded on the assumption that the abutment 
might be set in a pit without greatly disturbing the surrounding 
earth. If the horizontal component had been considered, the dif¬ 
ference between the lines of resistance according to the two theories 
would bave been still greater. Notice that the analysis which 
recognizes the existence of the horizontal forces, i. e., the rational 
theory, permits a lighter abutment than the theory which assumes 
the external forces to be entirely vertical. 

The omission of the horizontal components assumes that the 
only object of the abutment is to resist the thrust of the arch ; and 
that consequently the flatter the arch the greater the thrust and the 
heavier the abutment. Ordinarily the abutment must resist the 
thrust of the arch tending to overthrow it and to slide it outivcird, 
and must act also as a retaining wall to resist the lateral pressure of 
the earth tending to overthrow it and to slide it inward. For 
large arches the former is the more important ; but for small 
arches, particularly under high embankments, the latter is the more 
important. Hence, for large arches or for an arch having a light 
surcharge, the abutment should be proportioned to resist the thrust 
of the arch; but for small arches under a heavy surcharge of 
earth, the abutment should be proportioned as a retaining wall 
(Chap. XIV). 





494 


ARCHES. 


[CHAP. XVIII. 


Although the horizontal pressure of the earth can not be com¬ 
puted accurately, there are many conditions under which the 
horizontal components should not be omitted. For example, if the 
abutment is high, or if the earth is deposited artificially behind it, 
ordinarily it would be safe to count upon the pressure of the earth 
to assist in preventing the abutment from being overturned out¬ 
wards. Finally, although it may not always be wise to consider the 
earth pressure as an active force, there is always a passive resistance 
which will add greatly to the stability of the abutment, and whose 
intensity will increase rapidly with any outward movement of the 
abutment (see last paragraph of § 666). 

For empirical rules for the dimensions of abutments, see §§ 
722-23. 


Art. 2. Rules Derived from Practice. 

713. In the preceding article it was shown that every theory of 
the arch requires certain fundamental assumptions, and that hence 
the best theory is only an approximation. Further, since it is prac¬ 
tically impossible, by any theory (g 693), to include the effect of 
passing loads, theoretical results are inapplicable when the moving 
load is heavy compared with the stationary load. It was shown 
also that the stability of a masonry arch does not admit of exact 
mathematical solution, but is to some extent an indeterminate 
problem. At best the strains in a masonry arch can never be com¬ 
puted anything like as accurately as those in metallic structures. 
However, this is no serious matter, since the material employed in 
the former is comparatively cheap. 

Considered practically, the designing of a masonry arch is 
greatly simplified by the many examples furnished by existing 
structures which afford incontrovertible evidence of their stability 
by safely fulfilling their intended duties, to say nothing of the 
history of those structures which have failed and thus supplied 
negative evidence of great value. In designing arches, theory 
should be interpreted by experience ; but experience should be 
studied by the light of the best theory available. 

This article will be devoted to the presentation of current prac¬ 
tice as shown by approved empirical formulas and practical rules, 
and by examples. 



ART. 2.] 


RULES DERIVED FROM PRACTICE. 


495 


714. Empirical Formulas. Numerous formulas derived from 
existing structures have been proposed for use in designing masonry 
arches. Such formulas are useful as guides in assuming propor¬ 
tions to be tested by theory, and also as indicating what actual 
practice is and thus affording data by which to check the results 
obtained by theory. 

As proof of the reliability of such formulas, they are frequently 
accompanied by tables showing their agreement with actual struct¬ 
ures. Concerning this method of proof, it is necessary to notice 
that (1) if the structures were selected because their dimensions 
agreed with the formula, nothing is proven; and (2) if the struct¬ 
ures were designed according to the formula to be tested, nothing 
is proven except that the formula represents practice which is 
probably safe. 

At best, a formula derived from existing structures can only 
indicate safe construction, but gives no information as to the degree 
of safety. These formulas usually state the relation between the 
principal dimensions ; but the stability of an arch can not be de¬ 
termined from the dimensions alone, for it depends upon various 
attendant circumstances,—as the condition of the loading (if earth, 
upon whether loose or compact; and if masonry, upon the bonding, 
the mortar, etc.), the quality of the materials and of the workman¬ 
ship, the manner of constructing and striking the centers, the 
spreading of the abutments, the settlement of the foundations, etc. 
The failure of an arch is a very instructive object lesson, and should 
be most carefully studied, since it indicates the least degree of 
stability consistent with safety. Many masonry arches are excessively 
strong; and hence there are empirical formulas which agree with 
existing structures, but which differ from each other 300 or 400 per 
cent. All factors of the problem must be steadily borne in mind in 
comparing empirical formulas either with each other or with theo¬ 
retical results. 

A number of the more important empirical formulas will now be 
given, but without any attempt at comparisons, owing to the lack 
of space and of the necessary data. 

715. Thickness of the Arch at the Crown. In designingan arch, 
the first step is to determine the thickness at the crown, i. e., the 
depth of the keystone. 



496 


AKCHES. 


[CHAP, xviji. 


Let d = the depth at the crown, in feet; 

p = the radius of curvature of the intrados, in feet; 
r = the rise, in feet; 
s = the span, in feet. 

716. American Practice. Traut wine^s formula for the depth 
of the keystone for a first-class cut-stone arch, whether circular or 
elliptical, is 

d = y P+^ s ’ -|_ 0.2.(27) 

“For second-class work, this depth may be increased about one 
eighth part; and for brick work or fair rubble , about one third.” 

717. English Practice. Rankine’s formula for the depth of 
keystone for a single arch is 

d = V 0.12 p ;.(28) 

for an arch of a series , 

d = V0.17 p ;.(29) 

and for tunnel arches, where the ground is of the firmest and safest, 

d = y 0.12 A,.(30) 

and for soft and slipping materials, 

d- \ 0.48^-.(31) 

The segmental arches of the Rennies and the Stephensons, which 
are generally regarded as models, ‘‘ have a thickness at the crown 

of from y V to yV of span, or of from to -fo of the radius of 
the intrados.” 

718. French Practice .* Perronnet, a celebrated French engi¬ 
neer, is frequently credited with the formula, 

d = IjV + (32) 

* From “Proportions of Arches from French Practice,” by E. Sherman Gould 
in Van Nostrand’s Engin’g Mag., vol. xxix,p. 450. 

















ART. 2.] 


RULES DERIVED FROM PRACTICE. 


497 


as being applicable to arches of all forms—semi-circular, segmental, 
elliptical, or basket-handled,—and to railroad jn’idges or arches 
sustaining heavy surcharges of earth. “Perronnet does not seem, 
however, to have paid much attention to the rule ; but has made 
his bridges much lighter than the rule would require." Other 
formulas of the above form, but having different constants, are also 
frequently credited to the same authority. Evidently Perronnet 
varied the proportions of his arches according to the strength and 
weight of the material, the closeness of the joints, the quality of 
mortar, etc.; and hence different examples of his work give differ¬ 
ent formulas. 

DejardnPs formulas, which are frequently employed by French 
engineers, are as follows : 

For circular arches, 


if -= U d = 1 + 0.1/);.(33) 

s 

if -= i, cl = 1+ 0.05 p; .... (34) 

s 

if - = $, d = 1 + 0.035 p; ... . (35) 
s 

if - = *> d = l + 0.02p; .... (36) 

s 


For elliptical and basket-handled arches, 

if -= i, d= 1 + 0.07 p .(37) 

s 

Croizette-Desnoyers, a French authority, recommends the fol¬ 
lowing formulas : 

if -> d = 0.50 + 0.28 VYp'; . . . (38) 

s 

if -= d = 0.50 + 0.26 VYp'; . . . (39) 

s 

if -= d = 0.50 + 0.20 VYp-, . . . f40) 

s 







498 


ARCHES. 


[CHAP. XVIII. 


719. Notice that in none of the above formulas does the char¬ 
acter of the material enter as a factor. Notice also that none of 
them has a factor depending upon the amount of the load. 

Table 62 is given to facilitate the comparisons of the preceding 
formulas with each other and with actual structures. Values not 
given in the table can be interpolated with sufficient accuracy. It is 
remarkable that according to all formulas credited to Perronnet the 
thickness at the crown is independent of the rise, and varies only 
with the span. Notice that by Dejar din’s formulas the thickness 
decreases as the rise increases,—as it should. 

TABLE 62. 

Comparison of Empirical Formulas for Depth of Keystone. 


Proportion of Rise to Span. 


Formula. 

Semi-circle. 

Rise 

Span 


Rise 
Span - 

A 












Span. 



Span. 



Span. 



10 

50 

100 

10 

50 

100 

10 

50 

100 

Trautwine’s, for first-class work 

.99 

1.98 

2.70 

1.11 

2.23 

3.09 

1.26 

2.57 

3.55 

“ second “ “ 

1.11 

2.23 

3.04 

1.25 

2.51 

3.43 

1.44 

2.89 

4.00 

“ third “ 

1.32 

2.64 

3.60 

1.48 

2.97 

4.12 

1.68 

3.42 

4.73 

Rankine’s. 

.77 

1.73 

2.45 

1.00 

2.25 

3.16 

1.25 

2 79 

3.95 

Perronnet’s. 

1.51 

3.26 

5.43 

1.51 

3.26 

5.43 

1.51 

3.26 

5.43 

Dejardin’s. 

1.50 

3.50 

6.00 

1.42 

3.07 

5.17 

1.26 

2.30 

2.60 

Oroizette-Desnoyers’s. 

1.38 

2.48 

3.30 

1.56 

2.86 

3.85 

1.62 

3.01 

4.05 


720. Thickness of the Arch at the Springing. Generally the 
thickness of the arch at the springing is found by an application of 
theory; and hence but few empirical formulas are given for this 
purpose. 

Trautwine gives a formula for the thickness of the abutment, 
which determines also the thickness of the arch at the springing 
(see § 722). 

“The augmentation of thickness at the springing line is made, 
by the Stephensons, from 20 to 30 per cent.; and by the Rennies, 

• ibout 100 per cent.” 

721. If the loads are vertical, the horizontal component of the 
compression on the arch ring is constant; and hence, to have the 
mean pressure on the joints uniform, the vertical projection of the 












































RULES DERIVED FROM PRACTICE. 


499- 


ART. 2.] 


joints should be constant. This principle leads to the following 
formula, which is frequently employed : The length , measured radi¬ 
ally, of each joint heticeen the joint of rupture and the crown 
should he such that its vertical projection is equal to the depth of 
the keystone. In algebraic language, this rule is 


l — d sec a, .(41) 

in which l is the length of the joint, d the depth at the crown, and 
a the angle the joint makes with the vertical. 

The length of the joint of rupture,* i. e., the thicknesss of the 
arch at the practical springing line, can be computed by the above 
formula. The following arc the values for circular and segmental 
arches : 


r 

If -> 

s 


1 

2 


r 

<< — — 


i 

IT > 


r 

(< — 


i 

8 ^ 


r 

ee — 


1_ 

1 0 j 


r 

<( _ 


tV > 


i =2.00 d; . 
I — 1.40 d ; . 

I — 1,24 d : 
l —■ 1.1 o d , . 

I- 1.10 rf. 


• » 



(43) 

(44) 

(45) 

(46) 


722. Thickness of the Abutment.f Trautwine's formula is 

t — 0.2 p-f 0.1 r + 2.0,.(47) 

in which t is the thickness of the abutment at the springing, p the 
radius, and r the rise,—all in feet. “ The above formula applies 
equally to the smallest culvert or the largest bridge—whether cir¬ 
cular or elliptical, and whatever the proportions of rise and span— 
and* to any height of abutment. It applies also to all the usual 
methods of filling above the arch, whether with solid masonry to 
the level of the top of the crown, or entirely with earth. It gives 
a thickness of abutment which is safe in itself without any back¬ 
ing of earth behind it, and also safe against the pressure of the 


* Concerning the method of determining the joint of rupture, see §§ 680-82. 
+ Fora theoretical discussion of this subject, see §§ 711-12. 







.500 


ARCHES. 


[CHAP. XVIII. 


earth when the bridge is unloaded. It gives abutments which 

■alone are safe when the bridge is loaded ; but for small arches, the 

# « 

formula supposes that earth will be deposited behind the abut¬ 
ments to the height of the roadway. In small bridges and large 
culverts on first-class railroads, subject to the jarring of heavy 
trains at high speeds, the comparative cheapness with which an 
excess of strength can be thus given to important structures has led, 
in many cases, to the nse of abutments from one fourth to one half 
thicker than those given by the preceding rule. If the abutment is 
<of rough rubble, add 6 inches to the thickness by the above formula, 
to insure full thickness in every part.”* 

To find the thickness of the abutment at the bottom, lay off, in 
Fig. 139, on = t as computed by the above equation ; vertically above 



n lay off an — half the rise ; and horizontally from a lay off ab = one 
forty-eighth of the span. Then the line bn prolonged gives the 
hack of the abutment, provided the width at the bottom, sp, is not 
less than two thirds of the height, os. “ In practice, os will rarely 
■exceed this limit, and only in arches of considerable rise. In very 
high abutments, the abutment as above will be too slight to sustain 
the earth pressure safely.”* 

To find the thickness of the arch, compute the thickness ce by 
equation (27), page 496, draw a curve through e parallel to* the 
intrados, and from b draw a tangent to the extrados; and then will 
bfe be the top of the masonry filling above the arch. Or, instead of 
drawing the extrados as above, find, by trial, a circle which will 
pass through b, e, and b f , the latter being a point on the left abut¬ 
ment corresponding to b on the right. 


* Trautwine’s Engineer’s Pocket-book. 














ART. 2.] 


RULES DERIVED PROM PRACTICE. 


501 


Trautwine’s rule, or a similar one, for proportioning the abut¬ 
ment and the backing is frequently employed. For examples, see 
Plates IV and V. 

723. RanMne says that in some of the best examples of bridges 
the thickness of the abutment ranges from one third to one fifth of 
the radius of curvature of the arch at its crown. 

The following formula is said to represent German and Russian 
practice , 

t = 1 + 0.04 (5 g + 4 h), .(48) 

in which h is the distance between the springing line and the top of 
the foundation. 

724. Dimensions of Actual Arches. Table 63 (pages 502-3) 
gives the dimensions of a number of actual structures, which, from 
their wide distribution and the frequency with which most of them 
are cited as examples, may be taken to represent average practice. 
Unfortunately the details concerning most of them are very 
meager, the following and those in the table being all that can be 
obtained. 

No. 1 is the longest span ever built. 

No. 2 is the longest span in existence.* The arch is a circular 
arc of 110°. It carries a conduit (clear diameter 9 feet) and a car¬ 
riage-way (width 20 feet). The top of the roadway is 101 feet above 
the bottom of the ravine. The voussoirs are Quincy (Mass.) granite, 
and are 2 feet thick, 4 feet deep at the crown, and 6 feet at the 
springing. The spandrel filling is composed of Seneca sandstone, 
which, for a distance above the arch of 4 feet at the crown and 15 
feet at the springing, is laid in regular courses with joints radial to 
the intrados ; and hence the effective thickness of the arch is about 
8 feet at the crown and about 21 feet at the springing (see Fig. 159, 
page 525). The abutments are prevented from spreading by the 
bed-rock in the side-hills. 

No. 9 is a remarkable bridge. It was built by an “ uneducated” 
mason in 1750; and although a very rude construction, is still in 
perfect condition. A former bridge of the same general design at 
the same place fell, on striking the centers, by the weight of the 
haunches forcing up the crown ; and hence in building the present 
structure the load on the haunches of the arch was lightened bf 


* Concerning arched dams, see foot of page 330 and top of 331. 





502 


ARCHES 


[CHAP. XVIII.. 


TABLE 

Data Concerning 


Ref. 

No. 


Location and Description. 


1 

2 

3 

4 

5 

6 

7 

8 
9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 
21 

22 

oo 


25 

26 

27 

28 

29 

30 

31 

32 

33 

34 

35 

36 

37 

38 

39 

40 

41 

42 

43 

44 

45 

46 

47 

48 

49 

50 

51 

52 

53 

54 

55 

56 

57 

58 

59 

60 
61 


Trezzo, Italy; built in 1380, destroyed in 1427; granite. 

Cabin John, Washington (D. C.); aqueduct; granite (see § 724, p. 501). 

Grosvenor bridge, Chester, England.. 

Ballochmyle, over the Ayr, Scotland. 

London bridge, England; street; granite. . 

Gloucester, England. 

Turin, Italy. 

Alma bridge, Paris; small rough rubble in cement; railroad. 

Pont-y-Prydd, Wales; rough rubble in lime mortar (see § 724, p. 501). 

Maidenhead, England; brick in cement; railroad. 

Neuilly, France; five spans (see page 504). 

Bourbonnais Railway bridge; France; cut granite (see page 504). 

Waterloo bridge, London, England; granite. . 

Tonguelaud, England; turnpike. 

Napoleon bridge, Paris; small rough rubble in cement; railroad. 

Mantes, over Seine, France. 

Etherow river, England; railroad; four spans. 

Bishop Auckland, England; turnpike; built in 1388. 

Wellington bridge, Leeds, England. 

Louis XIX.. 

Dean bridge, near Edinburgh, Scotland; turnpike. 

Licking Aqueduct, Chesapeake & Ohio canal. 

Dorlaston... 

Over the Oise, France; railroad. 

Trilport, France; railroad. . 

Conemaugh viaduct, Pennsylvania R. R.; sandstone in lime (no sand). 

Royal Border viaduct, England; brick in cement. 

Posen viaduct. Germany; brick in cement. 

Orleans, France; railroad. 

Hutcheson bridge, Glasgow, Scotland. 

Falls bridge, Philadelphia & Reading R. R. 

St. Maxence, over the Oise, France. 

Westminster bridge, London. 

Allentown, England; turnpike. 

Staines, England: turnpike.” 

Black Rock Tunnel bridge, Philadelphia & Reading R. R. ...'. 

Edinburgh... 

Swatara, Philadelphia & Reading R. R.; brick. 

Brent R. R. viaduct, England; brick in cement. 

Wellesley bridge at Limerick. . 

Bow bridge, England; turnpike. 

Houghton river, England; railroad. 

Bewdly, England; turnpike. 

Chestnut Street bridge, Philadelphia; brick in cement . 

Carrollton viaduct, near Baltimore; railroad; granite. !..!!!!!!!!! 

Llanwast, in Denbighshire, Wales; built in 1636; turnpike. ”!.!!!!!!! 

Monocacy viaduct, Chesapeake & Ohio canal. ....!!!!!!!! 

Over the Forth, at Stirling. . 

Nemours, France... 

Abattoir Street, Paris; railroad. 

Dole, over the Doubs, France. !!!!!!!!!!!!!”! 

Chateau Thierry, France. .".."I!!”!”*. 

Avon viaduct, England; brick in cement. . . 

Filbert St., Extension Pennsylvania R. R., Philadelphia; brick in lime mortar 

James River aqueduct. Virginia.. 

Des Basses-Granges, Orleans h Tours, France. 

Over the Salat, France. 

Pesmes, over the Ougnon, France.. . 

Philadelphia & Reading R. R.. 

Couturette, Arbois, France. !.!.!. . 

Tonoloway culvert, under Chesapeake & Ohio canal; rubble in cement. 


* C = semi-circle ; E = elliptical; B = basket-handled. 







































































ART. 2.] 


RULES DERIVED FROM PRACTICE 


503 


63. 

Actual Arches. 


Ref. 

No. 


1 

2 

3 

4 

5 

6 

7 

8 
9 

to 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 
21 
22 

23 

24 

25 

26 

27 

28 

29 

30 

31 

32 

33 

34 

35 

36 

37 

38 

39 

40 

41 

42 

43 

44 

45 

46 

47 

48 

49 

50 

51 

52 

53 

54 

55 

56 

57 

58 

59 

60 
61 


Engineer, 


Meigs. 

Hartley... 
Miller. ... 
Rennie.... 
Telford. . 

Mosca. 

Darcel.... 
Edwards.. 
Brunei.... 
Perronnet 
Vaudray.. 
Rennie.... 
Telford... 
Couche... 

Haskoll... 

Rennie.... 
Perronnet, 
Telford.... 
Fisk. 


Stephenson 

Perronnet.. 
Labelye.... 
Stephenson 

Rennie. 

Robinson.. 

Mylne. 

Osborne.... 
Brunei. 

Walker.... 
Haskoll.... 

Telford- 

Kneass. 

Jones. 

Fisk. 

Perronnet.. 


Perronnet, 
Vignoles.. 

Ellet. 


Bertrand 
Steele.... 

Fisk. 


Curve 

of 

Intrados. 

Span. 

Rise. 

* 

feet. 

feet. 

.... 

251 

88 

C 

220 

57 

C 

200 

42 

c 

181 

90.5 

E 

152 

29.5 

E 

150 

35 

C 

148 

18 

E 

141 

28 

C 

140 

35 

E 

128 

24 

B 

128 

32 

C 

124 

6.92 

E 

120 

32 

C 

118 

38 

C 

116 

14.8 

E 

115 

34 

C 

100 

25 

C 

100 

22 

C 

100 

15 

C 

94 

9.75 

c 

90 

30 

c 

90 

15 

c 

87 

13 5 

c 

83 

11.75 

E 

81 

28 

c 

80 

40 

C 

80 

40 

C 

80 

16 

E 

79 

26.3 

C 

79 

13 

c 

78 

25 

c 

77 

6.40 

c 

76 

38 

c 

75 

11.50 

c 

74 

9.25 

c 

72 

16.5 

c 

72 

36 

c 

70 

25 

E 

70 

17.6 

E 

70 

17.5 

E 

66 

13.75 

C 

65 

32.5 

C 

60 

20 

C 

60 

18 

c 

58 

29 

c 

58 

17 

E 

54 

9 

C 

53 

10.25 

C 

53 

3.75 

C 

53 

5.11 

E 

52 

17.50 

E 

51 

17.0 

E 

50 

15 

C 

50 

7 

C 

50 

7 

C 

49 

24.5 

C 

46 

6.27 

C 

45 

3.83 

C 

44 

8 

C 

43 

6.13 

C 

40 

15 


Radius 

at 

Crown. 

Thickness. 

Crown. 

Spring¬ 

ing. 

feet. 

feet. 

feet. 

133 

4.00 


134 

4 t 

6 t 

140 

4.60 

7.00 

90 

4.50 

6.00 

162 

4.75 

9.00 

98 

4.50 


160 

4.92 


103 

4.92 

1.50 

88 

1.50 

169 

5.25 

7.16 

159 

5.13 


281 

2.67 

3.60 

112 

4.50 

8.CO 

65 

3.50 


120 

4.00 



6.40 



4.00 

4.00 


1.83 

1.83 


3.00 

7.00 


3.67 


49 

3.00 


75 

2.83 


76 

3 50 



4.60 



4.45 


40 

3.00 

3.50 

40 

2.66 


58 

4.66 



3.95 



3.50 

4.50 

43 

3.00 


119 

4.80 


38 

7.60 

14.00 


2.50 

3.00 


3.00 

6.00 

47 

2.75 

2.75 

36 

2.75 



3.50 

3.50 

44 

3.00 



2.00 


47 

2.50 



2.75 

2.75 

33 

2.20 


34 

2.50 


29 

2.50 

2.50 

33 

1.50 


45 

2.50 



2.75 



3.16 



2.97 



3.75 



3.75 


28.3 

2.00 



2.00 


47 

2.66 


24 

3.95 



3.63 

• 


3.83 


34 

2.50 



2.97 


21 

2.00 



t See § 720, and also Fig. 159, page 525. 




































































504 


ARCHES. 


[chap, xyiil 


leaving horizontal cylindrical openings (see third paragraph of 
§ 730) through the spandrel filling. The outer, or showing, arch 
stones are only 2.5 feet deep, and that depth is made up of two 
stones; and the inner arch stones are only 1.5 feet deep, and but 
from 6 to 9 inches thick. The stone quarried Avith tolerably fair 
natural beds, and received little or no dressing. It is a wagon-road 
bridge, and has almost no spandrel filling, the roadway being dan¬ 
gerously steep. A strain sheet of the arch shows that the line of 
resistance remains very near the center of the arch ring (see § 730). 
The mean pressure at the crown is about 244 pounds per square 
inch. On the whole it is an example of creditable engineering. 

No. 11, as designed, had a radius at the crown of 160 feet; but 
the arch settled 2 feet on removing the center, and increased the 
radius to about 250 feet. 

No. 12 is noted for its boldness. This design was tested by 
building an experimental arch—at Soupes, France—of the propor- 
tions given in the table, and 12 feet wide. The center of the ex¬ 
perimental arch was struck after four months, when the total set¬ 
tlement was 1.25 inches, due mostly to the mortar joints, which 
were about one quarter inch ; and it was not injured by a dis¬ 
tributed load of 500 pounds per square foot, nor by a weight of 5 
tons falling 1.5 feet on the key. 

No. 46 is said to have “ approached a horizontal line in conse¬ 
quence of the substitution of vehicles for pack-horses.” 

725. Table 63 affords some striking comparisons. For exam¬ 
ple, Nos. 8 and 9 have practically the same span ; and as the rise 
of the former is four fifths that of the latter, the thickness at the 
crown of the former should be only about one and a quarter times 
that of the latter, while in fact it is 3.3 times as thick. How¬ 
ever, the former carries a railroad, and the latter a turnpike ; but, 
on the other hand, the former is laid in cement, and the latter in 
lime. 

Nos. 11 and 12 have nearly the same*span, but the rise of the 
former is 4.7 times the latter ; and if the thickness at the crown 
were in like proportion—as it should be,—that of the former 
would be only 0.6 feet. Also compare No. 32 with No. 33 ; and 
No. 33 with Nos. 9 and 18. 

726. Dimensions of Abutments. For examples of the abutments 
of railway culverts, see Tables 49-52 (pages 425-31). Table 64,, 



ART. 2.] 


RULES DERIVED FROM PRACTICE. 


505 


below, gives the dimensions of a number of abutments represen¬ 
tative of French railroad practice. 

TABLE 64. 

Dimensions of Abutments from French Railroad Practice.* 


Ref. No. 

Designation of Bridge. 

Span. 

Rise. 

Depth of 

Keystone. 

Height of 

Abutment. 

Mean thick¬ 

ness of 
Abutment. 


Circular Arches. 

feet. 

feet. 

feet. 

feet. 

feet. 

1 

De crochet, chemin de fer de Paris & Chartres. 

13.2 


1.65 

13.20 

4.95 

2 

De Long-Sauts, chemin de fer de Paris 4 Chartres. 

16.5 


1.81 

9.90 

5.90 

3 

D’Enghien, chemin de fer du Nord.. 

24.4 


1.95 

6.60 

6.93 

4 

De Pantin, canal St. Martin. . 

27.0 


2.47 

11.85 

10.55 

5 

De la Bastille, canal St. Martin. 

36.3 


3.95 

20.75 

9.90 

6 

De Basses-Granges, Orleans it Tours. 

49.4 


3.95 

6.60 

12.50 

7 

Segmental Arches. 

Des Fruitiers, chemin du fer du Nord. 

13.2 

2.31 

1.81 

13.20 

5.94 

8 

De Paisia. 

16.5 

2.64 

1.72 

6.60 

5.61 

9 

De M6ry, chemin de fer du Nord. . 

25.2 

2.97 

2.14 

14.20 

11.71 

10 

De Couturette, at Arbois. 

42.9 

6.13 

2.97 

6.60 

17.16 

11 

Over the Salat. 

46.1 

6.27 

3.63 

24.49 

19.14 

12 

De la rue des Abattoirs, at Paris, chemin de fer de 
Strasbourg . . 

52.9 

5.11 

2.97 

12.96 

33.00 

13 

Over the Forth, at Stirling. 

53.5 

10.25 

2.75 

20.75 

16.00 

14 

St. Maxence, over the Oise. 

77.2 

6.40 

4.80 

27.85 

38.94 

15 

Over the Oise, chemin de fer du Nord . 

82.7 

11.75 

4.60 

17.90 

31.65 

16 

De Dorlaston. 

87.0 

13.50 

3.50 

16.55 

32.20 

17 

Elliptical or False-Elliptical Arches. 

De Charolles. 

19.8 

7.55 

1.95 

1.30 

5.25 

18 

Du Canal St Denis . 

39 5 

14.85 

17.10 

2.95 

3.75 

10.20 

13.65 

12 35 

19 

De Chateau-Thierry. 

51.3 

15.00 

20 

De Dole, over the Doubs . 

52.4 

17.50 

3.75 

1.35 

11.85 

21 

Wellesley, at Limerick. . 

70.0 

17.50 

2.00 

12.00 

16.50 

22 

D’Orleans, chemin de fer de Vierzon. 

79.5 

26.30 

3.95 

2.85 

18.40 

23 

De Trilport. 

80.7 

27.80 

4.45 

6.40 

19.30 

24 

De Nantes, over the Seine . 

115.2 

34.40 

6.40 

3.20 

28.90 

25 

De Neuilly, over the Seine. 

128.0 

32.00 

5.35 

7.55 

35.50 


727. Illustrations of Actual Arches.— For illustrations of 
stone arches for railroad culverts, see Plates II-V. Fig. 143 (page 509) 
shows a 50-foot stone arch on the Pennsylvania Railroad. For 
brick arches for sewers, see Figs. 148 and 149 (pages 513 and 514). 
For an example of a brick tunnel-arch, see Fig. 147 (page 512). 
Cabin John arch, the longest span in the world (see No. 2 of Table 
G3, page 502), is shown incidentally in Fig. 159 (page 525). 

728. Minor Details. Eacking, The backing is masonry of 
inferior quality laid outside and above the arch stones proper, to 
give additional security. The backing is ordinarily coursed or ran¬ 
dom rubble, but sometimes concrete. Sometimes the upper ends 


* E. Sherman Gould, in Van Nostrand’s Engin’g Mag., vol. xxix, p. 450. 

















































506 


ARCHES. 


[CHAP. XVIII. 


of the arch stones are cut with horizontal surfaces, in which case 
the backing is built in courses of the same depths as these steps 
and bonded with them. The backing is occasionally built in ra¬ 
diating courses, whose beds are prolongations of the bed-joints of 
the arch stones ; but it usually consists of rubble, laid in horizontal 
courses abutting against the arch ring, with occasional arch stones 
extending into the former to bond both together. The radial 
joints possess some advantages in stability and strength, particu¬ 
larly above the joint of rupture but below that joint the horizon¬ 
tal and vertical joints are best, since this form of construction the 
better resists the overturning of the arch outward about the 
springing line. Ordinarily, the backing has a zero thickness at or 
near the crown, and gradually increases to the springing line ; but 
sometimes it has a considerable thickness at the crown, and is pro¬ 
portionally thicker at the springing. 

It is impossible to compute the degree of stability obtained by 
the use of backing; but it is certain that the amount ordinarily 
employed adds very greatly to the stability of the arch ring. In 
fact, many arches are little more than abutting cantilevers ; and it 
is probable that often the backing alone would support the struct¬ 
ure, if the arch ring were entirely removed. 

729. Spandrel Filling. Since the roadway must not deviate 
greatly from a horizontal line, a considerable quantity of material is 

required above the backing to bring the 
roadway level. Ordinarily this space is 
filled with earth, gravel, broken stone, 
cinders, etc. Sometimes, tc save filling, 
small arches are built over the haunches 
of the main arch, as shown in Fig. 140. 
The interior longitudinal walls may be 
strengthened by transverse walls between 
them. To distribute the pressure uni¬ 
formly, the feet of these walls should 
be expanded by footings where they rest 
upon the back of the arch. 

730. I\ hen the load is entirely sta¬ 
tionary—as in an aqueduct or canal 
bridge—or nearly so—as in a long span 
arch under a high railroad embankment,—the materials of the 












ART. 2.] 


RULES DERIVED FROM PRACTICE 


507 


spandrel filling and the size and position of the empty spaces may 
be such as to cause the line of resistance to coincide, at least very 
nearly, with the center of the arch ring. 

For example, ABCD, Fig. 141, represents a semi-arch for which 
it is required to find a disposition of the load that will cause the 
line of resistance to coincide with the center line of the arch ring. 



D 


Fig. 141. 


Divide the arch and the load into any convenient number of divi¬ 
sions, by vertical lines as shown. From P draw radiating lines par¬ 
allel to the tangents of the center line of the arch ring at a, b, c, 
etc.; and then at such a distance from P that 01 shall represent, 
to any convenient scale, the load on the first section of the arch ring 
(including its own weight), draw a vertical line through 0. The 
intercepts 0-1, 1-2, 2-3, etc., represent, to scale, the loads which the 
several divisions must have to cause the line of resistance to coincide 
with the center of the arch ring. Lay off the distances 0-1, 1-2, 
etc., at the centers of the respective sections vertically upwards from 
the center line of the arch ring, and trace a curve through their 
upper ends. The line thus formed—JS^ 7 , Fig. 141—shows the re¬ 
quired amount of homogeneous load;' i. e., EF is the contour of the 
homogeneous load that will cause the line of resistance to pass ap¬ 
proximately through the center of each joint. 

Hence, by choosing the material of the spandrel filling and 





















508 


ARCHES. 


[CHAP. XVIIH 


arranging the empty spaces so that the actual load shall be equiv¬ 
alent in intensity and distribution to the reduced load obtained as 
above, the voussoirs can be made of moderate depth. The vacant 
spaces may be obtained by the method shown in Fig. 140 (page 
506) ; or by that shown in Fig. 142, in which A is a small empty 
cylindrical arch extending from the face of one end wall to that of 
the other. (See the description of arch No. 9, § 724, p. 501.) 

Notice that the lines radiating successively from P, Fig. 141 
(page 507), will intercept increasing lengths on the load-line ; and 
that, therefore, the load which will keep a circular arch in equilib¬ 
rium must increase in intensity per horizontal foot, from the crown 
towards the springing, and must become infinite at the springing of 

a semi-circular arch. Henco 
it follows that it is not practb 
cable to load a circular arch/ 
bevond a certain distance from 

%j 

the crown, so that the line of 
resistance shall coincide with 
the center line of the arch 
ring. 

731. Drainage. The drain¬ 
age of arch bridges of more 
than one span is generally ef¬ 
fected by giving the top sur¬ 
face of the backing a slight 
inclination from each side toward the center of the width of the 
bridge and also from the center toward the end of the span. The 
water is thus collected over the piers, from whence it is discharged 
through pipes laid in the masonry. 

To prevent leakage through the backing and through the arch 
sheeting, the top of the former should be covered with a layer of 
puddle, or plastered with a coat of best cement mortar (see § 141), 
or painted with coal tar or asphaltum (see § 264). 

732. For an illustration of the method of draining a series of 
arches, and also of several minor details not mentioned above, see 
Fig. 143, which represents “ Little Juniata bridge No. 12" on the 
Pennsylvania Railroad.* 


* Published by permission of Win. H. Brown, chief engineer. 



Fig. 142. 










BAse or bail 


ART. 2 .] 


RULES DERIVED FROM PRACTICE 


509 



Fig. 143.—Little Juniata Bridge No. 12, Pennsylvania R. R. 




































510 


ARCHES. 


[CHAP. XVIII. 


733. Brick Arches. The only matter requiring special mention 
in connection with brick arches is the bond to be employed. When 
the thickness of the arch exceeds a brick and a half, the bond from 
the soffit outward is a very important matter. There are three 
principal methods employed in bonding brick arches. (1) The arch 
may be built in concentric rings ; i. e., all the brick may be laid as 
stretchers, with only the tenacity of the mortar to unite the several 
rings (see Fig. 144). This form of construction is frequently called 
rowlock bond. (2) Part of the brick may be laid as stretchers and 
part as headers, as in ordinary walls, by thickening the outer ends 
of the joints—either by using more mortar or by driving in thin 
pieces of slate,—so that there shall be the same number of bricks in 




■each ring (see Fig. 145). This form of construction is known as header 
and stretcher bond, or is described as being laid with continuous 
radial joints. (3) Block in course bond is formed by dividing the 
arch into sections similar in shape to the voussoirs of stone arches, 
and laying the brick in each section with any desired bond, but 
making the radial joints between the sections continuous from 
intrados toextrados. With this form of construction, it is custom¬ 
ary to lay one section in rowlock bond and the other with radial 
joints continuous from intrados to extrados, the latter section being 
much narrower than the former (see Fig. 146). 

1. The objection to laying the arch in concentric rings is that, 
since the rings act nearly or quite independent of each other, the 
proportion of the load carried by each can not be determined. A 
ring may be called upon to support considerably more than its proper 
share of the load. This is by far the most common form of bonding 
in brick arches, and that this difficulty does not more often mani- 








ART. 2 .] 


RULES DERIVED FROM PRACTICE. 


511 


fest itself is doubtless due to the very low unit working pressure 
employed. The mean pressure on brick masonry arches ordinarily 
varies from 20 to 40 pounds per square inch, under which condition 
a single ring .might carry the entire pressure (see Tables 19 and 20, 
pages 164 and 166). The objection to this form of bond can be 
partially removed by using the very best cement mortar between 
the rings. 

The advantages of the ring bond, particularly for tunnel 
and sewer arches, are as follows: It gives 4-inch toothings for con¬ 
necting with the succeeding section, while the others give only 
2-inch toothings along much of the outline. It requires less 
cement, is more rapidly laid, and is less liable to be poorly executed. 
It possesses certain advantages in facilities for drainage, when laid 
in the presence of water. 

2. The objection to laying the arch with continuous radial joints 
is that the outer ends of the joints, being thicker than the inner, 
will yield more than the latter as the centers are removed, and 
hence concentrate the pressure on the intrados. This objection 
is not serious when this bond is employed in a narrow section 
between two larger sections laid in rowlock courses (see Fig. 146). 

3. When the brickwork is to be subject to a heavy pressure, 
some form of the block in course bond should be employed. For 
economy of labor, the e( blocks” of headers should be placed at such 
a distance apart that between each pair of them there shall be one 
more course of stretchers in the outer than in the inner ring ; but a 
moments consideration will show that this would make each section 
about half as long as the radius of the arch,—which, of course, 
is too long to be of any material benefit. Hence, this method 
necessitates the use of thin bricks at the ends of the rings. 

734. Examples of Brick Arches. The method of bonding shown 
in Fig. 146 (page 510) is frequently employed—as, for example, in 
the 70-foot brick arch of the Swatara bridge (Philadelphia and 
Reading R. R.), The bonding employed in arching the Vosburg 
tunnel (Lehigh Valley R. R.) is shown in Fig. 147 (page 512).* 

735. Fig. 148 (page 513) shows the standard forms of large 
brick sewers employed in the city of Philadelphia, f “ They are 

*From Rosenberg’s 44 The Vosburg Tunnel,” by permission, 
f R. Hering, in Trans. Am. Soc. of C. E., vol. vii, PP- 253-57. The illustrations 
are reproduced from those in the original, the force diagrams being omitted here. 






512 


ARCHES. 


[CHAP. XVIII. 


designed for a maximum pressure on the brick-work of 80 pounds 
per square inch,” which, considering the usual specifications for 
such work (see § 260, p. 176), seems unnecessarily small (see Tables 
19 and 20, pages 164 and 166). 

Fig. 149 (page 514) shows the standard forms of sewers in 
Washington, D. 0.* “The invert as shown is the theoretical form, 
although the concrete is rammed into the trench and nearly always 
extends beyond the limits shown.” The largest sewers have a trap- 
rock bottom; the intermediate sizes have a semi-circular vitrified 



pipe in the bottom ; and the smallest sizes consist of sewer pipes 
bedded in concrete. 

736 . Owing to their great number of joints, brick arches are 
liable to settle much more than stone ones, when the centers are re¬ 
moved ; and hence are less suitable than the former for large or flat 
arches. Nevertheless a number of brick arches of large span have 
been built (see Table 63, page 502). Trautwine gives the following 
description of some bold examples. “ On the Filbert Street exten¬ 
sion of the Pennsylvania R. R., in Philadelphia, are four brick arches 
of 50 feet span, and with the very low rise of 7 feet. The arch rings 
are 2j feet thick, except on their showing faces, where they are but 2 
feet. The joints are in common lime mortar, and are about J inch 


* Report of the Commissioners of the District of Columbia, for the year ending 
June 30, 1884, p. 175. For details of quantities of material required, and for esti¬ 
mates of cost, see report for preceding year, pp. 277-79. 


































ART. 2.J 


RULES DERIVED FROM PRACTICE 


513 

























































514 


ARCHES 


[CHAP. XVIII. 



Fig. 149.—Standard Forms of nrick Sewers.—Washington, D, C. 
































ART. 3.] 


CENTERS. 


515 


thick. These four arches, about 200 yards apart, with a large num¬ 
ber of others of 26 feet span, form a viaduct. The piers between 
the short spans are 4-[ feet thick, and those at the ends of the 50-foot 
spans are 18 \ feet. The road-bed is about 100 feet wide, giving room 
for 9 or 10 tracks. The springing lines of all the arches are about 
6 to 8 feet above the ground. One of the 50-foot arches settled 3 
inches upon permanently striking the center ; but no further settle¬ 
ment has been observed, although the viaduct has, since built (1880), 
had a very heavy freight and passenger traffic at from 10 to 20 miles 
per hour." 

737. Specifications for Stone Arches. The specifications for 
arch masonry employed on the Atchison, Topeka and Santa Fe 
Railroad are as follows : * 

738. First-Class Arch Masonry shall be built in accordance with the speci¬ 
fications for first-class masonry [see § 207], with the exception of the arch sheet¬ 
ing and ring stones. The ring stones shall be dressed to such shape as the 
engineer shall determine. The ring stones and the arch sheeting shall be not 
less than ten inches (10") thick on the intrados, and shall have a depth equal 
to the specified thickness of the arch. The joints shall be at right angles to 
the intrados, and their thickness shall not exceed three eighths of an inch (f' ). 
The face of the sheeting stones shall be dressed so as to make a close center¬ 
ing joint. The ring stones and sheeting shall break joints not less than one 
foot (1'). 

The wings shall be neatly stepped with selected stones of the full width of 
the wing, and of not less than ten inches (10") in thickness, overlapping by 
not less than one and one half feet (H'); or they shall be finished with a neatly 
capped newel at the end of each wing, and a coping course on the wing. The 
parapets shall be finished with a coping course of not less than ten inches 
(10") in thickness, having a projection of six inches (6 ')• 

739. Second-Class Arch Masonry shall be the same as first-class masonry (see 
§ 207). The stones of the arch sheeting shall be at least four inches (4") in thick¬ 
ness on the intrados ; shall have a depth equal to the thickness of the arch ; 
shall have good bearings throughout; and shall be well bonded to each othei 
and to the ring stones. 

740. Specifications for Brick Arches. See §§ 260-61 (pages 
176-77). 

Art. 3. Arch Centers. 

741. A center is a temporary structure for supporting an arch 
while in process of construction. It usually consists of a number of 
frames (commonly called ribs) placed a few feet apart in planes 

* For general specifications for railroad masonry, see Appendix I. 






516 


ARCHES. 


[CHAP. XVIII. 


perpendicular to the axis of the arch, and covered with narrow 
planks (called laggings) running parallel to the axis of the arch, 
upon which the arch stones rest. The center is usually wood— 
either a solid rib or a truss,—but is sometimes a curved rolled-iron 
beam. In a trussed center, the pieces upon which the laggings rest 
are called back-pieces. The ends of the ribs may be supported 
by timber struts which abut against large timbers laid upon the 
ground, or they may rest upon a shoulder on the abutment. 

The framing, setting up, and striking of the centers (§§ 752-55) 
is a very important part of the construction of any arch, particularly 
one of long span. A change in the shape of the center, due to 
insufficient strength or improper bracing, will be followed by a 
change in the curve of the intrados and consequently of the line of 
resistance, which may endanger the safety of the arch itself. 

742. Load to be Supported. If there were no friction, the load 
to be supported by the center could be computed exactly ; but fric¬ 
tion between the several arch stones and between these and the 
center renders all formulas for that purpose very uncertain. 
Fortunately, the exact load upon the center is not required ; for the 
center is only a temporary structure, and the material employed in 
its construction is not entirely lost. Hence it is wise to assume 
the loads to be greater than they really will be. Some allowance 
must also be made for the accumulation of the material on the 
center and for the effect of jarring during erection. The following 
analysis of the problem will show roughly what the forces are and 
why great accuracy is not possible. 

To determine the pressure on the center, consider the voussoir 
DEFG, Fig. 150, and let 

a = the angle which the joint BE makes 
with the horizontal; 

p. = the co-efficient of friction (see Table 36, 
page 315), i. e., p. is the tangent of! 
the angle of repose; 

6 = the angular distance of any point from 
the crown ; 

W = the weight of the voussoir DEFG ; 

N = the radial pressure on the center due to 
the weight of DEFG. 

If there were no friction, the stone DEFG would be supported 



Fig. 150. 






ART. 3.] 


CENTERS. 


517 


by the normal resistance of the surface DE and the radial reac¬ 
tion of the center. The pressure on the surface DE would then 
be W cos a, and the pressure in the direction of the radius W sin a. 

Friction causes a slight indetermination, since part of the weight 
of the voussoirs may pass to the abutment either through the arch 
ring or through the back-pieces (perimeter) of the center. Owing 
to friction, both of these surfaces will offer, in addition to the 
above, a resistance equal to the product of the perpendicular pres¬ 
sure and the co-efficient of friction (foot-note, page 276). If the 
normal pressure on the joint DE is W cos a , then the frictional 
resistance is /* IF cos a. Any frictional resistance in the joint DE 
will decrease the pressure on the center by that amount; and conse¬ 
quently, with friction on the joint DE, the radial pressure on the 
center is 


N = W (sin a — /i cos a) .(49) 

On the other hand, if there is friction between the arch stone and 
the center, the frictional resistance between these surfaces will 
decrease the pressure upon the joints DE, as computed above ; and 
consequently the value of N will not be as in equation (49). 

Notice that in passing from the springing toward the crown the 
pressure of one arch stone on the other decreases. Near the crown 
this decrease is rapid, and consequently the friction between the 
voussoirs may be neglected. Under this condition, the radial pres¬ 
sure on the center is 


N = W cos 6 , 



As a rough approximation, equation (50) may be applied for 
the first 30° from the crown, although it gives results slightly 
greater than the real pressures; and for the second 30°, equation 
(49) may be employed, although it gives results less than the actual 
pressure ; and for the third 30°, the arch stones may be considered 
self-supporting. 

743. The value of the co-efficient to be employed in equation 
(49) is somewhat uncertain. Disregarding the adhesion of the 
mortar, the co-efficient varies from about 0.4 to 0.8 (see Table 36, 





518 


ARCHES. 


[CHAP. XVIII. 


page 315) ; and, including the adhesion of good cement mortar, it 
may be nearly, or even more than, 1. (It is 1 if an arch stone 
remains at rest, without other support, when placed upon another 
one in such a position that the joint between them makes an angle 
of 45° with the horizontal.) If the arch is small, and consequently 
laid up before the mortar has time to harden, probably the smaller 
value of the co-efficient should be used ; but if the arch is laid up 
so slowly that the mortar has time to harden, a larger value could, 
with equal safety, be employed. As a general average, we will 
assume that the co-efficient is .58, i. e., that the angle of repose 
is 30°. 

Notice that by equation (49) N = 0, if tan a — yi ; that is to 
say, N = 0, if a = 30°. This shows that as the arch stones are 
placed upon one another they would not begin to press upon the 
center rib until the plane of the lower face of the top one reaches 
an angle of 30° with the horizon. 

Table 65 gives the value of the radial pressure of the several por¬ 
tions of the arch upon the center; and also shows the difference 
between applying equation (49) and equation (50). Undoubtedly 
the former should be applied when the angle of the lower face of 
any arch stone with the horizontal does not differ greatly from 30°; 
and when this angle is nearly 90°, then equation (50) should be ap¬ 
plied. It is impossible to determine the point at which one equation 
becomes inapplicable and the other applicable ; but it is probably 
safe to apply equation (49) up to 60° from the horizontal. 

744. Example. To illustrate the method of using Table 65, 
assume that it is required to find the .pressure on a back-piece of a 
20-foot semi-circular arch which extends from 30° to 60° from the 
horizontal, the ribs being 5 feet apart, and the arch stones being 2 
feet deep and weighing 150 pounds per cubic foot. Take the sum 
of the decimals in the middle column of Table 65, which is 3.19. 
Tins must be multiplied by the weight of the arch resting on 2° of the 
center. (In this connection it is convenient to remember that an 
arc of 1° is equal to 0.0175 times the radius.) The radius to the 
middle of the voussoir is 11 feet, and the length of 2° of arc is 0.38 
feet. The volume of 2° is 0.38x5x2 = 3.8 cubic feet; and the 
weight of 2° is 3.8x150 = 570 pounds. Therefore the pressure 
on the back-piece is 570x3.19 = 1,818 pounds. 




ART. 3.] 


CENTERS. 


519 


TABLE 65. 

The Radial Pressure of the Arch Stones 
of a Semi-Arch, on the Center. 


Angle of the Lower 
Face with the 

Radial Pressure in Terms of the 
Weight of the Arch Stone. 

Horizontal. 

By Equation (49). 

By Equation (50). 

30° 

0.00 


32° 

0.04 

( 

34° 

0.08 


36° 

0.12 


38° 

0.16 


40° 

0.20 


42° 

0.24 

0.67 

44° 

0.28 

0.69 

46° 

0.32 

0.72 

48° 

0 36 

0.74 

50° 

0.40 

0.76 

55° 

0.45 

0.82 

60° 

0.54 

0.86 

65° 

• • • • 

0.91 

70° 

• • • • 

0.94 

80° 

• • • • 

0.98 

90° 

• • • * 

1.00 


745. Outline Forms of Centers. Solid Wooden Rib. For 

flat arches of 10-foot span or under, the rib may consist of a plank, 
a, a , Fig. 151, 10 or 12 inches wide and 1^ or 2 inches thick, set 



edgewise, and another, b, of the same thickness, trimmed to the 
curve of the intrados and placed above the first. The two should 
be fastened together by nailing on two cleats of narrow boards as 
shown. These centers may be placed 2 or 3 feet apart. 






























520 


ARCHES. 


[CHAP. XVIII. 


746. Built Wooden Rib. For flat arches of 10 to 30 feet span, 

the rib may consist of two or 
three thicknesses of short 
boards, fitted and nailed (or 
bolted) together as shown in 
Fig. 152. An iron plate is 
often bolted on over the joints 
(see Fig. 147, page 512), which 
adds materially to the rigidity 
of the rib. Centers of this 
form have an astonishing strength. Trautwine gives the two fol¬ 
lowing examples which strikingly illustrate this. 

in the first of these examples, this form of center was employed 
for a semi-circular arch of 35 feet span, having arch stones 2 feet 
deep. “ Each rib consisted of two thicknesses of 2-incli plank, in 
lengths of about 6.5 feet, treenailed together so as to break joint. 
Each piece of plank was 12 inches deep at the middle, and 8 inches 
at each end, the top edge being cut to suit the curve of the arch. The 
treenails were 1.25 inches in diameter, and 12 of them were used to 
each length. These ribs were placed 17 inches apart from center to 
center, and were steadied together by a bridging piece of 1-inch 
board, 13 inches long, at each joint of the planks, or about 3.25 feet 
apart. Headway for traffic being necessary under the arch, there 
were no chords to unite the opposite feet of the ribs. The ribs were 
covered with close board-lagging, which also assisted in steadying 
them together transversely. As the arch approached about two 
thirds of its height on each side, the ribs began to sink at the 
haunches and rise at the crown. This was rectified by loading the 
crown with stone to be used in completing the arch, which was then 
finished without further trouble.” 

The other example was an elliptic arch of 60 feet span and 15 
feet rise, the arch stones being 3 feet deep at the crown and 4 feet 
at the springing. “Each frame of the centre was a simple rib 6 
inches thick, composed of three thicknesses of 2-inch oak plank, 
in lengths (about 7 to 15 feet) to suit the curve and at the same 
time to preserve a width of about 16 inches at the middle of each 
length and 12 inches at each of its ends. The segments broke 
joints, and were well treenailed together with from ten to sixteen 

















ART. 3.] 


CENTERS. 


521 


treenails to each length. There were no chords. These ribs were 
placed 18 inches from center to center, and were steadied against 
one another by a board bridging-piece, 1 foot long, at every 5 feet. 
When the arch stones had approached to within about 12 feet of 
each other, near the middle of the span, the sinking at the crown 
and the rising at the haunches had become so alarming that pieces 
of 12- X 12-inch oak were hastily inserted at intervals and well 
wedged against the arch stones at their ends. The arch was then 
finished in sections between these timbers, which were removed one 
by one as the arch was completed.” 

Although the above examples can not be commended as good 
construction—the flexibility of the ribs being so great as to endanger 
the stability of the arch during erection and to break the adhesion 
of the mortar, thus decreasing the strength of the finished arch,— 
they are very instructive as showing the strength attainable by this 
method. 

747. The above form of center is frequently employed, partic¬ 
ularly m tunnels, for spans of 20 to 30 feet, precautions being taken 
to have the pieces break joints, to secure good bearings at the 
joints, and to nail or bolt the several segments firmly together. 
The centers for the 25-foot arch of the Musconetcong (N. J.) tun¬ 
nel (Lehign Valley E. E.) consisted of segments of 3-inch plank, 
5 feet 8 inches long, 14 inches wide at the center, and 8 inches at 
the ends, bolted together with four ^-inch and four f-inch bolts 
each, and 14- X 8-inch pieces of plate-iron over the joints. Where 
the center was required to support the earth also, a three-ply rib 
was employed; but in other positions two-ply ribs, spaced 4 to 5 
feet apart, were used. Centers of this form have successfully stood 
very bad ground in the Musconetcong and other tunnels;* and 
hence we may infer that they are at least sufficiently strong for any 
ordinary arch of 30 feet span. 

Although not necessary for stability, it is wise to connect the 
feet of the rib by nailing a narrow board on each side, to prevent 
the end of the rib from spreading outwards and pressing against the 
masonry—thus interfering with the striking of the center,—and also 
to prevent deformation in handling it. 


* Drinker’s Tunneling, p. 548. 





522 


AKCHES. 


[CHAP. XVIII. 


748. Braced Wooden Rib. For semi-circular arches of 15 to 30 
feet span, a construction similar to that shown in Fig. 147 (page 512) 
may be employed. The segments should consist of two thicknesses 
of 1- or 2-inch plank, according to span, from 8 to 12 inches wide 
at the middle, according to the length of the segments. The hori¬ 
zontal chord and the vertical tie may each be made of two thick¬ 
nesses of the plank from which the segments are made. 

For greater rigidity, the rib may be further braced by any of 
the methods shown in outline in Figs. 153, 154, 155, or by obvious 





modifications of them. The form to be adopted often depends upon 
the passage-way required under the arch. Fig. 153 is supported by 
a post under each end; in extreme cases. Fig. 154 may be supported 
at the middle point also; and Fig. 155 may be supported at both 
middle points as well as at the ends. 

Since the arch masonry near the springing does not press upon 
the center, it may be laid with a template before the center is set 
up; and hence frequently the center of a semi-circular arch does 
not extend down to the springing line. For examples, see Figs. 
147 and 158 (page 512 and 524). 

Center frames are put together on a temporary platform or the 
floor of a large room, on which a full-size drawing of the rib is first 
drawn. 


749. Trussed Center. When the span is too great to employ 
any of the centers described above, it becomes necessary to construct 
trussed centers. It is not necessary here to discuss the principles 



of trussing, or of finding the strains in the several pieces, or of 
determining the sections, or of joining the several pieces,—all of 




















































ART. 3.] 


CENTERS. 


523 


which are fully described in treatises on roof and bridge construe- 
tion. There is a very great variety of methods of constructing such 
centers. Figs. 156 and 157 show two common, simple, and efficient 
general forms. 

750. Camber. Strictly, the center should be constructed with 
a camber just equal to the amount it will yield when loaded with 
the arch; but, since the load is indeterminate, it is impossible to 
compute what this will be. Of course, the camber depends upon 
the unit strain in the material of the center. The rule is frequently 
given that the camber should be one four-hundredth of the radius; 
but this is too great for the excessively heavy centers ordinarily 
used. It is probably better to build the centers true, and guard 
against undue settling by giving the frames great stiffness; and 
then if unexpected settling does take place, tighten the striking 
wedges slightly. 

The two sides of the arch should be carried up equally fast, to 
prevent distortion of the center. 

751. Examples of Actual Centers. For an example of a 
center employed in a tunnel, see Fig. 147 (page 512). 

Fig. 158 (page 524) shows the center designed for the 60-foot 
granite arches of the recently completed Washington bridge over 
the Harlem River, New York City.* The bridge is 80 feet wide, 
and fifteen ribs were employed. Notice that the center does not 
extend to the springing line of the arch; the first fifteen feet of 
the arch were laid by a template. 

Fig. 159 f (page 525) shows the center employed in constructing 
the Cabin John arch, which carries the Washington (D. C.) aque¬ 
duct over a creek, and which is the largest masonry arch in the 
world (see No. 2, Table 63, page 502). The arch is 20 feet wide, 
and five ribs were employed. 

752. Striking the Center. The Method. The ends of the ribs 
or center-frames usually rest upon a timber lying parallel to, and 
near, the springing line of the arch. This timber is supported by 
wedges, preferably of hard wood, resting upon a second stick, which 
is in turn supported by wooden posts—usually one under each end of 
each rib. The wedges between the two timbers, as above, are used 

* Published by permission of Wm. R. Hutton, chief engineer, 
t Compiled from photographs taken during the progress of the work (1856-60), by 
courtesy of Gen. M. C. Meigs, chief engineer. 





524 


ARCHES. 


[CHAP. XVIII* 


7 



£ "4Sr„Q/r.(? 


Fig. 158.—Center for 60-foot Granite Arches of Washington Bridge, Harlem River, New York City. 













































ART. 3.] 


CENTERS. 


525 



mm 

JHt wjuj 


SSS55W 


Fig. 159.—Cabin John Arch and Center, Washington (D. C.) Aqueduct.—For explanatory text see § 724 and § 751 (pages 501 and 523). 


























































































































































































ARCHES. 


[CHAP. XVIII. 


526 


in removing the center after the arch is completed, and are known 
as striking wedges . They consist of a pair of folding wedges—1 to 
2 feet long, 6 inches wide, and having a slope of from 1 to 5 to 1 to 
10—placed under each end of each rib. It is necessary to remove 
the centers slowly, particularly for large arches ; and hence the 
striking wedges should have a very slight taper,—the larger the span 
the smaller the taper. 

The center is lowered by driving back the wedges. To lower 
the center uniformly, the wedges must be driven back equally. 
This is most easily accomplished by making a mark on the side of 
each pair of wedges before commencing to drive, and then moving 
each the same amount. 

753. Instead of separate pairs of folding wedges, as above, a 
compound wedge, Fig. 160, is sometimes employed. The pieces 



Fig. 160. 


A and B are termed striking plates. The ribs rest upon the former, 
and the latter is supported by the wooden posts before referred to. 
The wedge C is held in place during the construction of the arch 
by the keys, A, A, etc., each of which is a pair of folding wedges. 
To lower the center, the keys are knocked out and the wedge C is 
driven back. 

The piece C is usually as long as the arch, and supports one end 
of all the ribs ; but with large arches, say 80 to 100 feet span, it is 
customary to support each rib on a compound wedge running 
parallel to the chord of the center (perpendicular to the axis of the 
arch). Instead of cutting the striking plates A and B as shown in 
Fig. 160, the compound wedge may play between tapered blocks 
gained into A and B. The piece C is usually made of an oak 
stick 10 or 12 inches square. The individual wedges are from 4 to 
6 feet long. 

For the larger arches, the compound wedge is driven back 
with a heavy log battering-ram suspended by ropes and swung 
back and forth by hand. The inclined surfaces of the wedges 







CENTERS. 


527 


ART. 3.] 

should be lubricated when the center is set up, so as to facilitate 
the striking. 

754. An ingenious device, first employed at the Pont d'Alma 
arch—141 feet span and 28 feet rise,—consisted in supporting the 
center-frames by wooden pistons or plungers, the feet of which 
rested on sand confined in plate-iron cylinders 1 foot in diameter 
and about 1 foot high. Near the bottom of each cylinder there was 
a plug which could be withdrawn and replaced at pleasure, by means 
of which the outflow of the sand was regulated, and consequently 
also the descent of the center. This method is particularly use¬ 
ful for large arches, owing to the greater facility with which the 
center can be lowered. See Fig. 158, page 524. 

755. The Time. There is a great difference of opinion as to the 
proper time for striking centers. Some hold that the center should 
be struck as soon as the arch is completed and the spandrel filling 
is in place; while others contend that the mortar should be 
given time to harden. It is probably best to slacken the centers as 
soon as the keystone is in place, so as to bring all the joints under 
pressure. The length of time which should elapse before the centers 
are finally removed should vary with the kind of mortar employed 
(see Fig. 5, page 89) and also with its amount. In brick and rubble 
arches a large proportion of the arch ring consists of mortar; and 
if the center is removed too soon, the compression of this mortar 
might cause a serious or even dangerous deformation of the arch. 
Hence the centers of such arches should remain until the mortar 
has not only set, but has attained a considerable part of its ultimate 
strength (see Fig. 5, page 89),—this depending somewhat upon the 
maximum compression in the arch. It is probable that a knowledge 
of the elasticity and of the “set” of mortar would give some light 
as to the best time to strike centers ; but unfortunately our infor¬ 
mation on those topics is very limited (see § 146). 

Frequently the centers of bridge arches are not removed for 
three or four months after the arch is completed ; but usually the 
centers for the arches of tunnels, sewers, and culverts are removed 
as soon as the arch is turned and, say, half of the spandrel filling is 
in place. 






APPENDIX I 


SPECIFICATIONS FOR MASONRY* 


Contents. 

General Railroad Masonry . .page 529 

Masonry for Railroad Buildings.. 534 

Architectural Masonry.. . . . .*. “ 539 

Baying Masonry in Freezing Weather.*_“ 543 


Railroad Masonry, f 

General Provisions. All stone used for the different classes of masonry 
must be furnished from the best quarries in the vicinity, subject to the ap¬ 
proval of the engineer. Brick masonry shall at all times be substituted for 
stone, when so desired by the engineer. 

Inspection. All materials will be subject to rigid inspection, and any that 
have been condemned must be immediately removed from the site of the work. 
The work will be done under the supervision of an inspector, whose duties 
will be to see that the requirements of these specifications are carried out; but 
his presence is in no way to be presumed to release in any degree the responsi¬ 
bility or obligation of the contractor. 

Laying Masonry. All classes of masonry laid in cement must be neatly 
pointed with cement mortar, finely tempered. No masonry of any kind must 
be covered until it has been inspected and accepted by the engineer. No ma¬ 
sonry will be allowed to be laid in freezing weather. [Many specifications 
omit this condition. See “ Specifications for Laying Masonry in Freezing 
Weather,” page 543.] 

Measurement of Masonry. All masonry and brick-work will be built ac¬ 
cording to the plans and instructions furnished by the engineer, and will be 
estimated and paid for by the cubic yard, computing only the actual solidity 
thereof. No constructive or conventional measurement will be allowed, any 
rule or custom in the section of the country through which the road passes to 
the contrary notwithstanding. The price per cubic yard paid for masonry 
and brick-work will include the furnishing of all material, scaffolding, cen¬ 
tering, and all other expenses necessary to the construction and completion of 
the masoury or brick-work. All “ dressed ” or “cut-stone” work—such as 
copings, bridge-seats, cornices, belt-courses, water-tables, brackets, corbels, 
etc.—furnished under the plans of the engineer will be paid for by the cubic 
yard, under the classification of the masonry in which they occur, with an 
additional price per square foot of the entire superficial surface of the stones 
“ dressed,” or “ cut,” or “ bush-hammered ” 

Allowance for Extras. No allowance will be made for timber, or work on 
same, used in scaffolding, shoring, or centering for arches,—excepting only 
timber, sheet-piling, or foundation plank, necessarily, and by order of the en¬ 
gineer, left in the ground. No allowance will be made to the contractor for 

* See also the specifications in the body of the bo k. See “Specifications ’ in Index. 

+ These specifications are the same, except in form, as those employed in the construction, 
•of the “ W4st Shore” Railroad, but do not differ materially from those used in other roads r 
and have frequently been accepted as the standard. 


529 











530 


SPECIFICATIONS FOR MASONRY. 


[APP. I. 


any damage he may sustain by reason of floods or other causes; but such 
draining, bailing, or pumping from foundations as the engineer may decide to 
be necessary will be paid for at a price to be fixed by the engineer. 

First-class Masonry will consist of quarry-faced ashlar [see §§200-07] 
laid in horizontal courses having parallel beds and vertical joints, of not less 
than ten inches (10") nor more than thirty inches (30") in thickness,—decreas¬ 
ing in thickness regularly from the bottom to the top of the wall,—laid flush 
in cement mortar of the quality hereinafter specified. Each course must be 
thoroughly grouted before the succeeding one is laid. 

Size of Stones. Stretchers must be not less than two and one half feet (2^') 
nor more than six feet (6') in length, and not less than one and one half feet 
(1-$-') in width, nor less in width than one and one half (14) times their depth. 
Headers must not be less than three and one half feet (34') nor more than four 
and one half feet (4|') in length—where the thickness of the wall will admit 
of the same,—and not less than one and one half feet (H') in width, nor less 
in width than they are in depth of course. 

Cutting. Every stone must be laid on its natural bed. All stones must 
have their beds well dressed, parallel and true to the proper line, and made al¬ 
ways as large as the stone will admit of. The beds and sides of the stone must 
be cut, before being placed on the work, so as to form joints not exceeding one 
half inch (£") in width. No hammering on a stone will be allowed after it is 
set; but if any inequalities occur, they must be pointed off. The vertical 
joints of the face must be not less than eight inches (8") in from the face, and 
as much more as the stone will admit of. All corners and batter lines must be 
run with a neat chisel draft one and one half inches (1£") on each face. The 
projections of the quarry face beyond the draft lines must not exceed four inches 
(4"); and in the side-walls of tunnels this projection must not exceed two 
inches (2"). 

Bond. The masonry shall consist of headers and stretchers alternating. At 
least one fourth of it shall consist of headers extending entirely through the 
wall, and every header shall be immediately over a stretcher of the underlying 
course. The stones of each course shall be so arranged as to form a proper 
bond—in no case less than one foot (1')—with the stones of the underlying course. 

Backing. The backing shall be of good-sized, well-shaped stones, laid so 
as to break joints and thoroughly bond the work in all directions, and leave no 
spaces between them over six inches (6") in width, which spaces shall be filled 
with small stones and spalls well grouted. 

Coping. All bridge-seats and tops of walls will be finished with a coping 
course of such dimensions and projections as may be ordered by the engineer, 
dressed and cut to a true surface on top and front edges, in conformity with 
diagrams for same which will be furnished by the engineer. 

Foundation Courses. All foundation courses must be laid with selected 
large flat stones, not less than twelve inches (12") thick, nor of less superficial 
surface than fifteen (15) square feet. 

Second-class Masonry [§§208-12] will consist of broken range rubble 
of superior quality, laid with horizontal beds and vertical joints on the face, 
with no stone less than eight inches (8") in thickness—unless otherwise directed 
by the engineer,—well bonded, and leveled as well as can be without hammer- 
dressing. No mortar joint shall exceed three quarters of an inch (£") in thick¬ 
ness. All corners and quoins shall have hammer-dressed beds and joints; and 
all corners and batter lines shall be run with an inch-and-one-half (1£") chisel 
draft. At least one fourth (£) of the stones in the face must be headers evenly 
distributed through the wall. 

Bridge-seats and tops of walls shall be coped in the same manner as specified 
for first-class masonry. Stones in foundation courses shall be not less than 
twelve inches (12") thick, and shall contain not less than twelve (12) square 
feet of surface. 



RAILROAD MASONRY. 


531 


Third-class Masonry will consist of good substantial rubble [§§213-17] 
laid in cement mortar. All stones shall be perfectly sound, and sufficiently 
large to make good, well-bonded, strong work; and shall be laid on their 
natural beds, in the most substantial manner, and with as much neatness as 
this description of work admits of. The stones in the foundations must be not 
less than ten inches (10") thick, and shall contain not less than ten (10) square 
feet of surface; and each shall be firmly, solidly, and carefully laid. 

First-class Arch-culvert Masonry shall be built in accordance 
with the specifications for first-class masonry, with the exception of the arch 
sheeting and the ring-stones. The rings shall be dressed to such size and 
shape as the engineer shall direct. The ring-stones and sheeting-stones shall 
not be of less thickness than ten inches (10") on the intrados, and shall be 
dressed with three eighths inch (-§") joints, and shall be of the full depth speci¬ 
fied (by drawings or otherwise) for the thickness of the arch. The joints must 
be made on truly radial lines, and the face of the sheeting-stones must be 
dressed to make close joints with the center. The ring-stone and sheeting- 
stones shall break joints by not less than one foot (1'). 

The wing walls shall be neatly stepped, in accordance with the drawings 
furnished, with selected stones of the full width of the wing and of not less 
than ten inches (10") in thickness, no stone being covered less than eighteen 
inches (18") by the one next above it; or the wing shall be finished with a 
neatly capped newel at the end, and a coping course,—as may be selected by 
the engineer. The parapet shall be finished with a coping course of full width 
of parapet, with such projection as may be directed by the engineer, the stone 
to be not less than ten inches (10") thick. 

Second-class Arcli-culvert Masonry shall be of the same general 
character and description as second-class masonry, with the exception of the 
ring-stones and the arch sheeting. The former shall be dressed as specified 
for first-class arch-culvert masonry. The latter shall consist of selected stones 
of the full depth of the arch, and shall have a good bearing throughout the 
thickness of the arch, and shall be well bonded. No stone shall be less than 
six inches (6") in thickness on the intrados. 

Box-culvert Masonry will be good rubble [see §§ 213-17], neatly laid 
up with square-shaped stones of a size and quality satisfactory to the engineer. 
The end parapet walls and also the side walls for three feet (3 ) from the ends 
shall be laid in good cement mortar. When box culverts are ordered to be 
laid up entirely in cement mortar [see § 214], they will be classified as third- 
class masonry, and must conform to the specifications for the same. 

The covering-stone for all box culverts shall be not less than ten inenes 
(10") in thickness, and must have a good, solid, well-leveled bearing on the 
side walls of not less than fifteen inches (15"). 

Vitrified Pipe. In localities where but a small quantity of water passes, 
vitrified pipe will be substituted for culverts when so ordered by the engineer. 
Sizes of twelve (12"), fifteen (15"), or eighteen (18") inches in diameter may be 
used, and must be of the best quality double strength, vitrified culvert pipe, 
subject to the approval of the engineer. Vitrified pipes must be well and care¬ 
fully bedded and laid [see Figs. 97-99, pages 409-10], in accordance with the 
instructions of the engineer. 

Retaining 1 Walls will be classified as second- or third-class masonry 
laid dry, as may be ordered in each particular case. 

Slope Walls will be of such thickness and slope as directed by the en¬ 
gineer. The stones must reach entirely through the wall, and be not less than 
four inches (4") thick and twelve inches (12") long, laid with close joints,and 
as free as possible from spalls. The foundations must be prepared and laid as 
directed by the engineer. 

Stone Paving shall be made by setting on edge stone from eight (8 ) to. 




532 


SPECIFICATIONS FOR MASONRY. 


[APP. I. 


fifteen inches (15") in depth, laid either dry or grouted with strong cement 
mortar, as may be directed by the engineer. 

Riprap. When required by the engineer, the face of embankments and 
the foot of slopes shall be protected from the action of water by a facing of 
riprap stone, or of brush and stones, or by a retaining wall, as may be directed. 
The riprap, when used, shall be laid by hand by competent workmen, and 
shall be of such thickness and slope and of such undressed stone as the en¬ 
gineer may direct 

Brick Masonry. The brick must be of the best quality [see § 57], 
well tempered, hard burned, and 8£ X 4 X 2£ inches.* No bats, cracked, 
crooked, or salmon bricks will under any circumstances be allowed in the 
work. The brick shall be well soaked in water before being laid, and shall 
be laid in hydraulic cement mortar of the quality hereafter specified, with 
such thickness of joint and style of bond [§242 and §733] as shall be prescribed 
by the engineer. Grout will be substituted for mortar when ordered by the 
engineer. 

Brick arching must be covered on the back with a coat of strong cement 
mortar one inch (1") thick. In tunnel arching wherever a seam of water is 
met, the arch must be covered with roofing felt; or with a course of asphaltum 
(applied hot) of such thickness as may be directed by the engineer, and this 
covered with a plastering of cement mortar so as to make the arch impervious 
to water. A properly formed drainage channel shall be left in the backing of 
the arch and side walls, with suitable openings for the escape of the water, at 
such points and of such size as may be directed by the engineer. The keying 
of all arches shall be most carefully done, and in such manner as may from 
time to time be directed by the engineer. The packing between the arch and 
tunnel roof shall never be put in until at least forty-eight (48) hours after the 
section has been keyed. 

Cement. The cement must be of the best quality of freshly ground hy¬ 
draulic cement [of the Rosendale type—see § 72], aud be equal in quality to the 
best brands of . . . ... cement. It will be subject to test by the engineer or his 
appointed inspector, and must stand a tensile stress of fifty (50) pounds per 
square inch of sectional area on specimens allowed a set of thirty (30) minutes 
in air and twenty-four (24) hours under water [see § 90, and art. 5 of Chapter 
III]. 

Mortar. The mortar shall in all cases be composed of one (1) part in bulk 
of the above specified hydraulic cement to two (2) parts in bulk of clean, 
sharp sand, well and thoroughly mixed together in a clean box of boards, be¬ 
fore the addition of the water. It must be used immediately after being 
mixed; and no mortar left over night will, under any pretext, be allowed to 
be used. The sand and cement used will at all times be subject to inspection, 
test, and acceptance or rejection by the engineer. 

Concrete. The coucrete shall be composed of two (2) parts in bulk of 
hard, sound, and acceptable stone—broken to a size that will pass in any direc¬ 
tion through a two-inch (2") ring, thoroughly clean and free from mud, dust, 
dirt, or any earthy admixture whatever,—and one (1) part of freshly-made 
cement mortar of the quality above described. The concrete shall be quickly 
laid in sections, in layers not exceeding nine (9) inches in thickness, and shall 
be thoroughly rammed until the water flushes to the surface. It shall be al¬ 
lowed at least twelve (12) hours to set before any work is laid on it. 

Foundations. Excavations. Foundations for masonry shall be excavated 
to such depths as may be necessary to secure a solid bearing for the masonry, 
—of which the engineer shall be the judge. The materials'excavated will be 


* Instead of the dimensions as above, the specifications of which these are a revision and 
also many others contain the term 4 4 standard size,” but until recently that term could have 
had no special significance (see § 62, page 46). 








RAILROAD MASONRY. 


533 


classified and paid for, as provided for in the Specifications for Grading. All 
materials taken from the excavations for foundations, if of proper quality, 
shall be deposited in the contiguous embankment; and any material unfit for 
such purpose shall be deposited outside the roadway, or in such place as the 
engineer shall direct, and so that it shall not interfere with any drain or w T ater 
course. In case of foundations in rock, the rock must be excavated to such 
depth and in such form as may be required by the engineer, and must be 
dressed level to receive the foundation course. 

Artificial Foundations. When a safe and solid foundation for the masonry 
can not be found at a reasonable depth (of which the engineer is to be the 
judge), the contractor shall prepare such artificial foundations as the engineer 
may direct. 

Paving. Box culverts and small bridge abutments may have a paved foun¬ 
dation, if so directed by the engineer, by setting stones on edge, breaking 
joints, and extending across the entire width of the foundation. 

Timber. Timber foundations shall be such as the engineer may by drawings 
or otherwise prescribe, and will be paid for by the thousand feet, board meas 
ure.—the price to include the cost of material, framing, and putting in place. 
All timber must be sound, straight-grained, and free from sap, loose or rotten 
knots, wind shakes, or any other defect that would impair its strength or 
durability. It must be sawed (or hewed) perfectly straight and to exact 
dimensions, with full corners and square edges. All framing must be done 
in a thorough, workmanlike manner. Both material and 'workmanship will 
be subject to the inspection and acceptance of the engineer. 

Piling. All piles shall be of young, sound, and thrifty white oak, yellow 
pine or other timber equally good for the purpose, acceptable to the engineer. 
They must be at least eight inches (8") in diameter at the small end and twelve 
inches (12”) in diameter at the butt when sawn off; and must be perfectly 
straight and be trimmed close, and have the bark stripped off before they are 
driven. The piles must be driven into hard bottom until they do not move 
more than one half inch (-£-”) under the blow of a hammer weighing two thou¬ 
sand (2,000) pounds, falling twenty-five feet (25') at the last blow. They must 
be driven vertically and at the.distances apart, transversely and longitudinally, 
required by the plans or directions of the engineer. They must be cut off 
square at the butt and be well sharpened to a point; and when necessary, in 
the opinion of the engineer, shall be shod with iron and the heads bound with 
iron hoops of such dimensions as he may direct,—which will be paid for the 
same as other iron-work used in foundations. 

The necessary length of piles shall be ascertained by driving test piles in 
different parts of the localities in which they are to be used. In case a single 
pile shall not prove long enough to reach hard bottom, two shall be spliced 
together as follows: The head shall be sawed off square, and a hole two inches 
<2' j in diameter and twelve inches (12”) deep shall be bored into it; and into 
this hole a circular white oak treenail twenty-three inches (23”) in length shall 
be well driven. Then another pile similarly squared and bored, and of as 
large a diameter at the small end as can be procured, shall be placed upon the 
lower pile, brought to its proper position, and driven as before directed. All 
piles, when driven to the required depth, are to be cut off truly square and 
horizontal at the height given by the engineer; and only the actual number of 
lineal feet of the piles left for use in the foundations after being sawed off, 
will be paid for. 

Iron. All wrought and cast-iron work ordered by the engineer will be 
paid for by the pound,—the price to include the cost of material, manufac¬ 
ture, and placing in the work. 

Coffer-dams. Where coffer-dams are, in the opinion of the engineer, re¬ 
quired for foundations, the prices provided in the contract for timber, piles, 
and iron in foundations, will be allowed for the material and work on same, 




534 


SPECIFICATIONS FOR MASONRY. 


[APP. I.. 


which is understood as covering all risks from high water or otherwise, drain¬ 
ing, bailing, pumping, and all materials connected with the coffer-dams. 
Sheet-piling will be classed as plank in foundations; and if left in the ground 
will be paid for by the thousand feet (1,000), board measure. 


Railroad Buildings.* 

Tools. All tools necessary for the execution of the contract, including 
mortar boxes, will be furnished by the contractor at his own expense. 

Staging. All staging required for the execution of the work done under 
contract shall be furnished by the contractor at his own expense. The rail¬ 
way company will, however, upon the completion of any structure, purchase 
of the contractor such staging material as it can advantageously use, and pay 
the contractor for such material an amount which, in the opinion of the rail¬ 
way company’s engineer, shall seem reasonable and just. 

Ext* avatious. Dry excavations, or excavations above water, will be 
made by the contractor when so ordered by the railway company. Wet exca¬ 
vations, or excavations below water, will be made by the railway company, 
excepting when a special arrangement is made with the contractor. All exca¬ 
vations will be classified as either earth, loose rock, or solid rock. 

When the excavation for any structure is made entirely by the contractor, 
it shall be measured in cubic yards, and paid for at the price per cubic yard 
specified in the contract. When an excavation is made in part by the railway 
company’s force and is finished by the contractor’s force, or when contractor’s 
force assists railway company’s force in making any excavation, contractor will 
be paid for the actual time that his force is employed, at laborer’s current rate 
per day plus ten per cent. In case contractor furnishes a foreman for such 
work, time charged for foreman must not exceed one day for foreman for 
each ten days of labor, and contractor will be paid for the services of such 
foreman at a rate per day not to exceed the current wages paid foremen of 
laborers plus ten per cent. In case contractor uses masons, foremen of masons, 
or other skilled labor for the execution of the above “extra” or “time” work, 
the wages and time allowed will be the same as it would be if the work had 
been performed and supervised by laborers and foremen of laborers. When 
“extra” or “time” work is performed by contractor’s force, and is supervised 
by contractor’s foreman, who at the same time and place has charge of and 
is supervising “ contract ” work, no pay will be allowed contractor for such 
supervision, except when, in the opinion of the railway company’s engineer, 
it may seem reasonable and just. 

All excavations shall be made strictly in accordance with the plans fur¬ 
nished by the railway company and the stakes set by the railwaj' - company’s 
engineer, and shall be executed in a neat and workmanlike manner. Where 
excavations are made under the supervision of the contractor, his agent or 
foreman, any erroneous or unnecessary excavation, and any masonry conse¬ 
quent to such erroneous or unnecessary excavation, shall be entirely at the 
contractor’s expense, unless the contractor can show that such unnecessary 
work was caused by errors in the plans furnished by the railway company, or 
by errors in the railway company’s engineer’s stakes or instructions. 

When excavation is made for concrete, great care must be taken to make 
the pits or trenches, as the case may be, of the exact width and depth required 
for the concrete, and any unnecessary excavation made or concrete used on 
account of lack of such care on the part of the contractor will be at his ex¬ 
pense. Excavations for stone footing courses will be made, w r lien not other- 


Atcbiaon, Topeka and Santa F6 Railroad. 






RAILROAD BUILDINGS. 


535 


yise ordered, eighty inches (8") (four inches (4") on each side) wider than the 
footing course. Excavations for walls not having footing courses will be 
made, when not otherwise ordered, twelve inches (12”) (six inches (6”) on 
■each side) wider than the wall is thick. 

Before masonry is built, excavations must be cleared of all loose earth, 
mud, or other objectionable material. 

Stone. Stone will be furnished by the contractor at his own expense, and 
be of a quality suitable for the different classes of masonry hereinafter speci¬ 
fied, and be subject to the inspection and acceptance of the railway company’s 
engineer. Stone will be loaded on cars and unloaded by the contractor at his 
own expense. Stone will be delivered by the railway company on the nearest 
available side track to the work, and no charges whatsoever will be allowed 
contractor for hauling stone from cars to the work, except in extreme cases, 
where, in the opinion of the railway company’s engineer, such charges may 
appear reasonable and just. 

Sand. All sand for mortar or concrete will be furnished by the contractor 
at his own expense. When, in the opinion of the railway company’s engineer, 
sand can not be secured by contractor within reasonable distance by wagon 
haul and at a reasonable price, transportation by rail will be furnished by the 
railway company, it being optional with the railway company at what point 
sand shall be procured. When railway company furnishes transportation for 
sand, cars shall be loaded and unloaded by contractor at his own expense. 

All sand furnished by contractor shall be clean and sharp, and subject to 
the inspection of, and rejection by, the railway company’s engineer. When, 
in the opinion of the railway company’s engineer, sand requires screening, it 
shall be screened by the contractor at his own expense. 

Cement and Lime. All cement and lime will be furnished by the 
railway company at its own expense; and will be delivered on cars on the 
nearest available side track to the work. It shall be unloaded by the con¬ 
tractor at his own expense, and shall be piled up in such manner by him as the 
railway company’s engineer may direct. Cement and lime shall be covered 
and protected from the weather by the contractor at his own expense, in such 
manner as seems suitable to the railway company’s engineer; and the con¬ 
tractor will be held responsible for the value of any cement damaged on ac¬ 
count of unsuitable protection. 

Water. W r ater required for all work done under contract shall be fur¬ 
nished by the contractor at his own expense. No charges made by contractor 
for hauling water will be allowed. When, in the opinion of the railway com¬ 
pany’s engineer, water can not be procured by the contractor within reason¬ 
able wagon haul, or at a reasonable expense, it will be furnished by the rail¬ 
way company. 

Mortar. Except when otherwise ordered, all mortar shall be thoroughly 
mixed in a box, in the following proportions: One (1) part cement, two (2) 
parts sand, with sufficient water to render the mixture of the proper consist¬ 
ency. Care must be taken to thoroughly mix the sand and cement dry, in the 
proportions specified, before the introduction of water into the mixture. Mor¬ 
tar shall not be mixed except as it is used, and no mortar must be allowed to 
stand over night in mortar boxes or elsewhere. 

Concrete. All concrete shall consist of one (1) part cement, two (2) parts 
sand, and six (6) parts broken stone, together with sufficient water to mix the 
sand and cement to the consistency of good mortar for masonry. The pro¬ 
portion of sand, cement, broken stone, and the quantity of water used in the 
mixture, may be varied at the option of the railway company’s engineer. 

Stone shall be of a quality acceptable to the railway company’s engineer, 
and be broken so that seventy-five (75) per cent, will pass through a two-inch 
(2”) ring and so that all will pass through a two and one half inch (2-|”) 
ring. Broken stone shall be free from mud, dirt, and other objectionable 





536 


SPECIFICATION'S FOR MASONRY. 


[APP. I. 


material, and shall he subject to the inspection of, and rejection by, the rail¬ 
way company’s engineer. 

The sand and cement must be thoroughly mixed dry, in a clean, tight 
mortar box, before the introduction of water; and after water is applied to the 
mixture, the whole must be worked over with hoes until a good mortar of 
proper consistency is secured. After the mortar is made, the broken stone 
must be thoroughly drenched with clean water, and then shall be added to 
the mixture in the proportion stated above—or in any other proportion which 
the railway company’s engineer may specify. The concrete must then be 
worked over and mixed until each stone is completely covered with mortar 
and all spaces between the stones entirely tilled with same. 

The concrete shall be deposited in horizontal layers not exceeding twelve 
inches (12 ') in depth, and shall be thoroughly tamped when so required by the 
railway company’s engineer. 

Rubble Masonry. Rubble masonry will be classified as either heavy 
rubble, foundation rubble, pier rubble, or uncoursed hammer-squared rubble. 
The latter will be called for convenience squared rubble [see §§208-12]. 

Heavy Rubble. When not otherwise specified or shown on the plans, foot¬ 
ing courses will be built of rubble masonry. When footing courses exceed 
thirty inches (30 ') in width, the masonry will be classified as heavy rubble; 
and when thirty inches (30") or less in width, the masonry will be classified as 
foundation rubble. 

Heavy rubble footing courses shall be built of well-selected stone, which 
shall have a thickness not less than the height of the footing course. Each 
stone shall have a bottom bed of good surface over its entire area, which shall 
be horizontal when the stone is in position. As much of the upper surface of 
each stone as will be directly under the masonry to be put above the footing- 
course shall be uniform and parallel to the bottom bed. At least one third (^) 
of the length of the footing course shall be built of through-stone, and a 
larger proportion shall be furnished by the contractor when, in the opinion 
of the railway company’s engineer, more through-stone are required to secure 
stability. No stone shall be used which will not bond or extend under the 
masonry to be built above the footing course a distance equal to at least one 
third (}) the thickness or width of the masonry; and not more than two stones 
shall be used at any section to make up the total width of the footing course, 
and the exposed face of each stone shall be at least twelve inches (12") in length. 

All stones must be roughly jointed with a hammer for a distance back 
from their faces equal to the projection or offset of the footing course. No 
spaces to exceed forty (40) square inches in area shall be filled with spalls or 
chips, and the total area of all spaces must not exceed five (5) per cent, of the 
area of the footing course. 

All stone when placed in position must be thoroughly rammed until firmly 
embedded in a bed of mortar, which shall first be placed in bottom of excava¬ 
tion or trench, and after stone are placed in position, all joints must be well 
grouted with mortar. When so required by the railway company’s engineer, 
footing courses shall be built exactly to the dimensions shown on drawings or 
specifications, or with their edges built to a line. 

Foundation Rubble. In general, and when not otherwise specified, all masonry 
below the bottom of water table or below the top of rail for stone buildings, 
and all masonry below the sill of wooden buildings, will be classified as foun¬ 
dation rubble, except footing courses more than thirty inches (30") in width, 
which will be classified as heavy rubble. Foundation rubble may be required, 
however, for any portion or for all the masonry in any structure, in which 
case no additional price shall be allowed, except when, in the opinion of the 
railway company’s engineer, it shall seem reasonable and just. 

In this class of masonry no stone having an exposed face shall be less 
than one twenty-fourth (-fa) of a foot in cubical contents nor less than two 
inches (2") thick. Any stone smaller than this will be considered a spall; 


i 





RAILROAD BUILDINGS. 


53? 


and spalls are not to be used to exceed seven (7) per cent, of the entire mass. 
The contractor will not be required to furnish stone (except for through- 
stone) larger than one and one half feet (1^') in cubical contents, but the stone 
used shall not average less than one half (|) of a cubical foot in contents. No 
stone shall be used which does not bond, or extend into the wall, at least six 
inches (6"). One through-stone, whose face area shall not be less than one 
half (4) of a superficial foot, will be required for each sixteen (16) superficial 
feet of face measurement of wall, and more than this may be required by the 
railway company when, in the opinion of its engineer, a larger proportion of 
througli-stoue is required to secure stability; provided, however, that the con¬ 
tractor shall in no case be required to furnish through-stone to exceed ten (10) 
per cent, of the entire mass. At least twenty (20) per cent, of the entire ma¬ 
sonry shall consist of headers, or bond stones. In walls twenty-four inches 
(24 ') thick or less, these headers shall be at least two thirds (f) the thickness of 
the wall in length; and in walls more than twenty-four inches (24") thick, they 
shall be of sufficient length and be so placed as, in the opinion of the railway 
company’s engineer, seems necessary to secure well-bonded and stable work. 

Each stone shall be laid in its quarry bed, and any stone set on edge, or 
with the planes of its stratification vertical, will be rejected and ordered re¬ 
moved at the expense of the contractor. Stones shall be firmly bedded in 
mortar, and all spaces and joints thoroughly grouted with same. 

Pier Rubble. Piers or pedestals whose horizontal sectional area is nine (9) 
square feet or less will be classified as pier rubble. When this area exceeds 
nine (9) square feet, the masonry will be classed as foundation rubble. Foot¬ 
ing courses for such piers, when not exceeding sixteen (16) square feet in area, 
will be classed as pier rubble; and when exceeding this area, they will be 
classified as heavy rubble. 

Footing courses must be built, so far as practicable, in accordance with the 
preceding specifications for heavy rubble masonry. Masonry in piers above 
footing courses must be carefully built of well-selected stone, having horizon¬ 
tal beds and vertical joints, and be thoroughly bonded; corners and faces 
must be built true and plumb. The specifications for foundation rubble, so 
far as practicable, shall apply to this class of masonry. 

Each pier or pedestal shall be furnished with a hammer-dressed cap-stone 
not less than six inches (6") thick, of same area as pier, which must be accu¬ 
rately set at the required level. The price of this cap-stone must be included 
in the contract price per cubic yard for this class of masonry. 

Squared Rubble. When not otherwise specified, the walls of all stone build¬ 
ings above the bottom of the water-table will be built of uncoursed squared 

O 

rubble. 

In general the specifications for foundation rubble will apply to this class 
of masonry, the difference between the two classes being in the construction 
and finish of the outside face. The outside face of the wall will be built of 
well-selected stones, as nearly uniform in color as possible, which shall be 
neatly squared to rectangular faces, and which in all cases shall be laid on 
their natural or quarry beds. The beds of the stones shall be horizontal and 
the side joints vertical.“and no joints to exceed three fourths (f) of an inch will 
be allowed. No stone having a face area of less than eighteen (18) square 
inches or a thickness less than three inches (3") shall be used; and the average 
face of all the stones shall not be less than seventy-two (72) square inches. 

The inside face shall be built and finished in accordance with the specifica¬ 
tions for foundation rubble. 

Corners of all buildings shall be built up with quoin stones, uniform in size 
and arrangement, for which no extra pay will be allowed contractor. Drafts 
will be cut on the corners when so specified or shown on plans. All joints 
shall be cleaned or raked out for a distance of three quarters of an inch (|"), 
and neatly pointed with a raised joint,. The mortar used for pointing shall be 
composed of such material as the railway company’s engineer may select. 



538 


SPECIFICATIONS FOR MASONRY. 


[APP. I. 


Openings for windows, doors, or for other purposes, will be made in walls 
when specified or shown on plans. The jambs of such openings shall be 
neatly cut to a true and smooth surface, and be drove tooled, crandalled, or 
tooth-axed [see pages 125-34, particularly 123 and 133], as may be required 
by the railway company’s engineer. Bed-joints of jamb-stones must be care¬ 
fully cut, so that no joint to exceed one half an inch (■£") will appear on the 
exposed face of the jambs. Jamb-stones shall be uniform in height, and one 
half shall be through-stones. In general the arrangement of jamb-stones will 
be shown on drawings. 

The contract price for any opening shall include the cost of cut-stone sills, 
lintels, arches, jamb-stones, or any other cut-stone work required for that 
opening. In case no contract price is made for any opening, the contractor 
will be paid such price as, in the opinion of the railway company’s engineer, 
seems reasonable and just. 

Cut stone shall be furnished and put in place by the contractor when so re¬ 
quired by the railway company. The stone furnished shall be of the quality 
required for the work, and acceptable to the railway company’s engineer; and 
must be cut strictly^ in accordance with the plans and specifications in each 
case, and must be so cut as to lie, when in position, on natural or quarry beds. 
Cut stone will be paid for at the price specified in contract, and in case cut 
stone is furnished by the contractor for which there is no contract price, a 
price will be paid which, in the opinion of the railway company’s engineer, 
seems reasonable and just. 

Cut stone, or dimension stone for cut-stone work, may be furnished by the 
railway company at its own expense, and the contractor required to set the cut 
stone in position, or to cut and set the rough dimension stone, in winch case the 
■contractor will be paid for the work either as “extra”or “time” work, or at 
a price which, in the opinion of the railway company’s engineer, may seem 
reasonable and just. 

Wall Masonry. All walls shall be built to a line both inside and out¬ 
side, and both faces shall be finished with a smooth and uniform surface, 
which shall be flat-pointed with a trowel, in a neat and workmanlike manner. 

The upper courses of all walls, when leveled or finished for the reception of 
superstructure, shall be provided with a through-stone at each end, and also 
one tlirough-stone for at least each five (5) lineal feet of wall. These through- 
stone shall be dressed on their top beds and accurately set to a level one half 
inch (I") below the level of the bottom of the superstructure. Between these 
through-stone the walls must be carefully laid, with the upper beds of the 
stones brought up flush with the top of the above-described through-stones so 
as to secure a perfectly level surface for the top of the wall. In no case shall 
spalls or chips be used, except in vertical joints. 

The contractor w r ill make such openings in walls as are required for 
windows, doors, or other purposes. No additional pay will be allowed for 
such openings, except where jambs are to be cut, and cut-stone sills or lintels 
are required, in which case such price per opening will be allowed as, in the 
opinion of the railway company’s engineer, may seem reasonable and just. Cut 
or dressed dimension-stone will be furnished and set in position w r hen so re¬ 
quired by plans or specifications, and will be paid for by the railway company 
at such price as may, in the opinion of its engineer, seem reasonable and just. 
Wood, iron, or other material which may be required to be built into the ma¬ 
sonry shall be properly put into position by the contractor, and no extra pay 
shall be allowed for such work. The cubical contents of such material, how¬ 
ever, will not be deducted from the measurement of the masonry. 

When so required, the contractor shall plaster the outside surface of base¬ 
ment or other walls with hydraulic mortar, composed of such materials as the 
railway company may select, and for such work the railway company will pay 
the contractor a price per square yard in addition to the contract price of the 
masonry. 





ARCHITECTURAL MASONRY. 


539 


Foundations for Trestles. Foundations for trestle bents, such as are 
built for coal chutes, will be classified as foundation rubble, and must be built 
wilhgreat care. The lower footing course, when exceeding thirty inches (30") 
in width, will be classed as heavy rubble. The upper course shall have one 
hammer-dressed through-stone at each end of wall, and at least three such 
through-stones between the end through-stones; otherwise the top course will 
be finished in accordance witli the second paragraph Tinder “wall masonry” 
above. This does not apply to bent foundations inside of coal-chute build¬ 
ing, which will be built in the same manner as foundation walls in general. 

^ Well-wall Masonry. Well-walls will be classified as foundation rubble. 
Well masonry will be built under the supervision of the well foreman who has 
charge of the well excavation, and contractor’s foreman shall execute the work 
strictly in accordance with instructions given by him. When well-walls are 
sunk, or settled, as the excavation is made great care must be taken to make 
the outside surface perfectly smooth and uniform; and as many headers, not 
to exceed the maximum heretofore specified, may be required as, in the opin¬ 
ion of the railway company’s engineer or well foreman, are necessary to 
secure stability. 

Measurement of Masonry. Iu measuring masonry paid for by the 
cubic yard, all openings will be deducted, and the number of cubic yards 
will be the actual cubical contents of the masonry built. The cubical contents 
of cut stone, iron work, timber or other material, built into the masonry by the 
contractor, will not be deducted from the cubical contents of the whole mass. 


Architectural Masonry.* 


Permit. The contractor for the masonry shall take out a building per¬ 
mit, including water for himself and plasterer aud all other contractors that 
may require water about the building during the progress of the work. This 
contractor shall also take out street and obstruction permit, and permit for 
building curb and retaining walls. The cost of the above permits is to be in¬ 
cluded in the estimate. 

Grade. The inside grade at the building shall be such as the superintend¬ 
ent shall direct. At the time of starting any pier, this contractor shall ascer¬ 
tain from the superintendent the height the inside grade shall be set above the 
established outside grade, taking into consideration the settlement that may 
occur during the progress of the work. 

Excavation. It is the intention that this contractor shall call at the 
building and examine for himself the exact situation of the building site. He 
shall remove from the premises all earth or debris, except that which the super¬ 
intendent may consider good for use in the grading required about the build¬ 
ing. This contractor shall complete such grading about the building as may 
be found necessary. All sidewalk stone that may be found in connection with 
the excavation shall be removed by the mason, the said stone becoming his 
property. The same shall apply to any foundation stone or other material 
that may be found in excavating, although none of said material shall be used 
in connection with the new work about the building. 

This contractor shall excavate, according to drawings, for all walls, piers, 
areas, etc., the intention being that the general level shall be excavated simply 
to the level of the finished basement floor. All trenches shall be excavated to 
the neat size as near as practicable; and each shall be leveled to a line on the bot¬ 
tom, ready to receive the foundation. At such time as the superintendent shall 


* Except in form, these specifications are those employed by Burnham & Root, archi¬ 
tects, Chicago, for the Society of Savings Building, Cleveland, Ohio, and conform closely to 
the general form employed by these architects. 






540 


SPECIFICATIONS FOR MASONRY. 


[APP. I, 


direct, this contractor shall level off the basement surfaces and floors of areas 
to a line finishing three inches (3”) below the top of the level of the finished 
basement floors, and leave the surface ready to receive the work of other con - 
tractors. When considered necessary in the judgment of the superintendent, 
all earth shall be tamped solidly and then be wet. 

If any pockets of quicksand are found, this contractor shall excavate the 
same, and fill in solidly with concrete composed of clean broken stone of a size 
that will pass through a two-inch (2") ring and English Portland cement, pro¬ 
portioned 1 to 3, rammed solidly into place in the pockets, in layers, as the 
superintendent may direct. None of the sand that may be found while ex¬ 
cavating shall be used in connection with any of the work about the building. 

After all foundations or retaining walls are in and fixed, this contractor 
shall tamp the earth solidly around them, leaving it level to a line within 
eighteen inches (18") of the finished grade, and ready to receive the work of 
other contrach rs. 

Bailing. This contractor shall do all bailing and draining of trenches or 
basement surfaces that may be found necessary during the progress of the work. 

Shoring. This contractor shall protect all walls of the adjoining buildings, 
underpin all walls that may be considered necessary—in the judgment of the 
superintendent—to place the new work or to prevent injury of the old work, 
make good all repairs, provide such cutting as may be found necessary to 
place the work, and leave the adjoining buildings as good as at the start. The 
cost of this work is to be included in his estimate. This contractor shall 
furnish and put in place any sheet piling that may be required to retain the 
earth while the footings are being put in, and include all costs of the same in 
his estimates. 

Protection. This contractor shall use proper care and diligence in brac¬ 
ing and securing all parts of the work against storm, wind, and the action of 
frost. Every night during freezing weather, each pier or wall shall be covered 
on top with sail-cloth, and the covering shall extend down over the face of all 
• green work. 

Concrete Footings. This contractor shall provide a frame of the area 
of the pier, composed of two-inch (2") plank, so arranged that the parts can be 
withdrawn and the pier left isolated after the concrete is set [see $ 30<>]. All 
footings not otherwise indicated shall be constructed of concrete furnished by 
this contractor. The cement shall be first-quality, fresh Utica, or any other 
equally good quality approved by the architects. The contractor at the time 
of submitting his proposal shall state the kind of cement he intends using. 
The sand shall be clean and sharp. The stone shall be clean limestone, crushed 
to a size that will pass through a two-inch (2") ring, and screened. The con¬ 
crete shall be composed of these ingredients in the following proportions: one 
(1)part of hydraulic cement, one (i) part of sand, and two (2) parts of crushed 
limestone. The cement and sand shall be mixed dry, and the mixture wet 
with a quantity of water sufficient to reduce it to the consistency of mortar. 
The stone and mortar shall be thoroughly mixed and laid in trenches as soon 
as possible, in layers of not more than six inches (0") in thickness, and be 
rammed until the water rises freely to the top. 

All concrete footings shall be carefully leveled or pitched with concrete, 
and be left ready to receive the piers, walls, or columns, in each case as par¬ 
ticularly indicated on the drawings. 

Railroad-Rail Footings. All railroad rails that may be required in 
connection with the foundations shall be of Bessemer steel, weighing not less 
than sixty-five (65) pounds per yard, straight and sound, cut to the neat lengths 
indicated on the drawings. All railroad rails shall be furnished by this con¬ 
tractor, and by him set in place to centers and levels as indicated on the dia¬ 
grams. None of these railroad rails are to be painted. 

The concrete used in connection with steel-rail footings shall be composed 



ARCHITECTURAL MASONRY. 


541 


of one (1) part of first-quality English Portland cement—or any other equally 
good quality approved by the architects,—one (1) part of clean sharp sand, and 
two (2) parts of clean limestone crushed to chestnut size. This concrete shall 
be mixed as for concrete footings, and shall be rammed in solidly between the 
rails; and each tier shall be neatly squared at the outer edge. 

Rubble Masonry- All piers colored blue on the drawings shall be 
classed as cut stone, and shall be furnished and set in place by another con 
tractor; but all walls colored blue on the drawings—referring particularly to 
foundation walls for boiler-house, foundation wall for staircase way in alley, 
area walls, curb walls, and curtain walls between piers—shall be classed as rub¬ 
ble masonry, and shall be furnished and set in place by the mason. 

All stone used in connection with rubble masonry shall be of selected, large 
size, first-quality stone, laid to the lines on both sides, well fitted together and 
thoroughly pointed, frequent headers that extend through the wall being pro¬ 
vided. All stone shall be not less than two feet six inches (2' 6") long, one foot 
six inches (1' 6") wide, and eight inches (8") thick, except such as may be found 
necessary to level up a course to the required height. The intention is that all 
walls shall be laid in courses about one foot six inches (T 6") in height, 
leveled off at each course. Each stone shall have hammer dressed beds and 
joints, and shall be firmly bedded and be well cushioned into place. All 
joints shall be filled with mortar. The facing of all walls shall be laid ran¬ 
dom range, and the face of the stone shall be coarse bush-hammered. 

At the time of completing the retaining walls, this contractor shall excavate 
at least one foot (l 1 ) on the outside of the wall, and point up all joints on the 
outside; and then provide and apply a coat of first-quality English Portland 
cement, not less than a half inch (4") thick, to the outside of the wall from top 
to bottom. No cement covering will be required on the curb walls. All joints 
showing inside the building shall be raked out and neatly pointed up with 
cement; and, in addition, the face of walls coming in connection with the area 
shall be squared up. the joints finishing not to exceed one half inch (V') thick. 

All curb walls that may be required to receive the side-walks shall be 
brought to such levels as the superintendent shall direct, and shall be cemented 
on top and left ready to receive the.side-walks—which shall be furnished and 
set by another contractor. None of the screen walls shall be set in place until 
such time as the superintendent shall direct. The foundation for the staircase 
bay in the alley shall be set in place, after the building is partly completed, at 
such time as the superintendent may direct. This contractor, at the time of 
starting this work, shall furnish such anchors as may be considered neces¬ 
sary, in the judgment of the superintendent, to attach his work to that 
already in place, and shall do all cutting and fitting that may be found neces¬ 
sary to properly place his work. 

Mortar for Rubble Masonry. All rubble masonry above referred to shall 
be laid in mortar composed of perfectly fresh Utica cement—or other equally 
as good approved by the architects,—mixed in the proportion of one (1) part 
of cement to two (2) parts of clean sharp coarse sand. The sand and cement 
shall be mixed in a box dry; then wet, tempered, and immediately used. 

Common Brick-work. All walls or sections colored red on the draw¬ 
ings or otherwise indicated to be of brick, shall be of selected, first-quality, 
hard-burned Chicago sewer brick—or other equally good quality approved by 
the architects. The above quality of brick shall be used throughout the entire 
work, except that hollow fire-clay brick shall be used in connection with all 
curtains between windows on elevations above the first story, and for the back¬ 
ing of all stone-work above the top of the eighth-story floor beams. No bats 
shall be used. No pressed or face brick will be required in connection with 
this work. 

All brick shall be well wet, except in freezing weather, before being laid. 
Each brick shall be laid with a shove joint, in a full bed of mortar, all inter- 






.542 


SPECIFICATIONS FOR MASONRY. 


[APP. I. 


stices being thoroughly filled; and where the brick comes in connection with 
anchors, each one shall be “brought home” to do all the work possible. Up 
to and including the fifth story, every fourth course shall consist of a heading 
course of whole brick extending through the entire thickness of the walls; 
above the fifth story, every sixth course shall be a heading course. All mor¬ 
tar joints shall be neatly struck, as is customary for “ first-class trowel work.” 
All courses of brick-work shall be kept level, and the bonds shall be accurately- 
preserved. When necessary to bring any course to the required height, clip¬ 
ped courses shall be formed, as in no case shall any mortar joints finish more 
than one half inch (-£") thick. All brick-work shall be laid to the lines, and 
each tier kept plumb, the intention being that none of the window-frames shall 
be set in place until the roof is on. 

All lintels over openings indicated in connection with brick partition walls 
in basement shall be of steel railroad rails, and shall be furnished and set in 
place by the mason. These rails shall be painted one coat of mineral paint be¬ 
fore being brought to the building. 

All cut stone shall be backed as fast as the superintendent may consider 
proper, and the mason shall build in all anchors that may be furnished by the 
•contractor for the cut stone. When openings or slots are indicated in connec¬ 
tion with walls, the size and position of the same shall be such as the superin¬ 
tendent shall direct, unless otherwise shown. This contractor shall leave 
openings to receive all registers that may be required in connection with the 
heating or ventilating system, and shall also leave openings in connection with 
the corner vaults at such places in the floor and ceiling as the superintendent 
shall direct. 

All masonry that may be required at the time of setting the boilers shall be 
furnished and set in place by the contractor for steam-heating apparatus. 

Mortar for Brick-work. All mortar used in connection with sewer brick, 
together with the mortar in the brick parapet walls and the chimney above 
the roof line, shall be composed of two (2) parts of lime mortar—made up very 
poor,—and one (1) part of first-quality Utica cement—or other equally good 
approved by the architects. Said mortar shall be used immediately after being 
mixed, and in no case shall any be used that has stood over night. 

The remaining brick-work, including the fire-brick hereinafter referred to, 
shall be laid in mortar composed of best slaked lime and coarse sharp clean 
sand of approved quality. 

Brick Arches. Where arches are indicated in connection with the first- 
story banking vault or in connection with roadway in the court on the north 
front of building, said arches shall be formed with common brick laid in row- 
lock courses, regularly bonded [see § 733]. The mortar for this work shall con¬ 
sist of one (1) part Portland cement and three (3) parts clean sharp sand. Each 
brick shall be laid with a shove joint; and each rowlock course shall be 
cemented on top at the time of laying the next course. The last course shall 
be cemented on top, and be left ready to receive the concrete floor or roadway 
—which shall be provided by another contractor. 

All centers that may be required in connection with this work shall be 
furnished and set in place by the carpenter; and none of said centers shall be 
removed until such time as the superintendent shall direct. After the same 
have been removed, this contractor shall thoroughly clean down all face-work. 

All iron indicated in connection with this work shall be furnished and set 
in place by the contractor for constructional iron work,—except the bearing 
plates, which shall be bedded by the mason. 

Smoke Britching-. The smoke britching indicated in connection with 
the main boiler-stack will be furnished and set in place by the contractor for 
constructional iron, although the mason shall back up the same at such time 
.as the superintendent shall direct. 

Fire-brick. The lining shown to stand alone in connection with the 




ARCHITECTURAL MASONRY. 543 


boiler cnimney in the lower stories shall be laid with first-quality fire-clay 
brick, laid in stretcher courses, regularly bonded, with headers of whole brick 
sixteen inches (16") apart in every sixth course to stay the linings, care being 
taken to preserve the air-space indicated. 

All fire-clay brick shall be laid in first-class fire-clay mortar, each brick 
being laid with a solid joint neatly struck on each side with a trowel. 

Hollow Fire-clay Brick. All hrick used in connection with the 
spandrels above the first story on all elevations, together with all backing re¬ 
quired in connection with the stone work above the top of the eighth-story floor- 
beams, shall consist of first-quality, hard-burned, fire-clay, hollow brick, equal 
in quality to sample to be seen at the office of the architects. Each brick shall 
be laid with a shove joint. This contractor shall point up this work, and 
leave the surfaces of the walls smooth and ready to receive plastering. 

Cutting 1 and Fitting. This contractor shall do, promptly and at the 
time the superintendent so directs, all cutting and fitting that may be required 
in connection with the mason-work by other contractors to make their work 
come right, and shall make good after them. 

Setting Iron-work. It is the intention that all constructional iron¬ 
work shall be furnished and set in place by another contractor, and that all iron 
shall be hoisted from the outside of the building by means of a derrick. In 
setting the beams and columns in place, the mason shall keep pace with the 
contractor for constructional iron work, and at no time shall the mason be left 
one story behind the constructional iron-work. Each beam, girder, or column 
shown to rest on the masonry shall be provided with iron plates by the con¬ 
tractor for constructional iron, said plates being furnished to the mason at the 
sidewalk; and the mason shall set the same in place, firmly bedded in mortar, 
at such position or height as the superintendent shall direct. 

All iron wall-plates that may be required to receive the fire-clay arches 
will he furnished at the sidewaik by the constructional-iron contractor; and 
this contractor shall set each in such position and at such height as the super¬ 
intendent shall direct. 

Cut Stone. All parts colored blue on the drawings, or otherwise indi¬ 
cated to be of stone, or usually classed as cut stone, shall be furnished and set 
in place by the contractor for cut stone. The same shall apply for the terra¬ 
cotta roof-copings indicated. All mortar, staging, or hoisting apparatus that 
may be required in connection with this work shall be furnished by the con¬ 
tractor for cut stone. All cut stone will be set from the outside; but the 
mason shall back up all cut-stone work in a manner approved by the 
superintendent. 



APPENDIX II. 


SUPPLEMENTARY NOTES. 

Note 1. Labor Required in Quarrying.* The following table shows the 
labor required in quarrying the stone [gneiss] for the Boyd’s Corner dam on 
the Croton River near New York City. The stone to be cut was split out with 
plugs and feathers. 


Labor Required in Quarrying Gneiss. 


Kind of Labor. 

Days per Cubic Yard. 

Rough stone. 

Stone to be cut. 

Foreman. 

0.041 

0.114 

Drillers. 

0.339 

0.917 

Laborers . 

0.140 

0.429 

Blacksmiths. 

0.036 

0.102 

Tool-boy. 

0.0:35 

0.108 

Teams. 

0.141 

0.620 

Labor loading teams. 

0.077 

0.284 


Note 2. Cost of Cutting Granite.f “ Below is given the cost of cutting 
several kinds of masonry for the New York Department of Docks, in 1874-5. 
Between December 1878 and May 1875 with an average force of 40 stone¬ 
cutters, 2,065 yards of granite of the following kinds were cut in the Depart¬ 
ment yard: 

“ 1,524 yards of dimension stone were cut into headers and stretchers. 
This stone was cut to lay pinch beds and joints, the faces being pointed work, 
with a chisel draft 1 pinches wide. The headers averaged 2 feet on the face ,by 
8 feet in depth; and the stretchers averaged 6 feet long by 2 feet deep, the rise 
being 20, 22, and 26 inches for the different courses. The average time of 
stone-cutter cutting one cubic yard was 4.58 days of 8 hours; and the average 
cost of cutting was $27.54 per cubic yard ($1.02 per cubic foot). 

“ 810 yards of. coping were cut to lay pinch beds and joints, pointed on 
the face with chisel draft same as headers and stretchers, and 8-cut patent- 
hammered on top. with a round of 3| inches radius, the dimensions being 8 
feet long, 4 feet wide, and 2| feet .rise. The average time of stone-cutter 
cutting one cubic yard was 6.26 days, and the average cost of cutting $38.07 
per cubic yard ($1.41 per cubic foot). 

“231 yards of springers, keystones, etc., for arched pier at the Battery, 
were cut. These stones were of various dimensions, part being pointed work 
and part 6-cut patent-hammered. The average time of stone-cutter cutting 
one cubic yard was 6.88 days, and the average cost of cutting was $41.85 per 
cubic yard ($1.55 per cubic foot). 

“ The above cost of cutting includes, besides stone-cutter’s wages, labor of 
moving stone, all material used—such as timber for rolling stone, new tools, 
etc..—sharpening tools, superintendence, and interest on stone-cutter’s sheds[ 
blacksmith shop, derrick, and railroad. These expenses, in percents, of the 
total cost of cutting, are as follows: superintendence 5; sharpening tools 15; 
labor rolling stones 30; interest on sheds, derrick, and railroad 1; new 

* J. James R. Croes, in Trans. Am. Soc. of C. E., Vol. III., page 363 
t From an article by Wm. W. Maolay, in Trans. Am. Soc. of C. E., Vol. IV., pp. 310-11. 

544 
























APP. II.] 


SUPPLEMENTARY NOTES. 


545 


tools and timber for rolling stone 1; total 52 per cent., which, added to the 
wages paid stone-cutters, gives the total cost. During the last year stone¬ 
cutters were required to do at least 12 superficial feet per day of beds and 
joints, or its equivalent in pointed or fine cut work. The average day’s work 
of each stone-cutter, during one year and a half in which 118,383 superficial 
feet of beds and joints were cut, was 13.6 square feet per day, for which he 
received $4.00. 

“ The following table shows the amount of granite that a stone-cutter can 
cut in a day of 8 hours. 

Labor Required in Cutting Granite. 



Number of Superficial Feet 

Kind of Work. 

Constituting a 
day’s work of 8 
hours in stone- 
yards and con- 
tract-workdone 
in vicinity of 
New York City. 

Required as a 
minimum 
day’s work 
by the De¬ 
partment of 
Docks, New 
York. 

Averaged per 
day of 8 hours 
by stone-cut¬ 
ters in the 
Departm ent 
of D ocks, 
New York. 

Beds and joints. 

Pointed work with chiseled margin, lines 

16 

12 

13.6 

all round. 

10 

7.5 

8.5 

Pean-hammered. 

7.27 

5.45 

6.15 

6 cut patent-hammered. 

6.15 

4.61 

5.22 

8-cut “ “ . 

4 

5 

3.75 

4.24 


Note 3. Cost of Cutting Granite.* The average day’s work of a man 
in cutting the face of granite pitch-faced, range, squared-stone masonry 
(§ 197, page 137) of the Boyd’s Corner dam, as deduced from three and a half 
years’ work in which 5,200 cubic yards were cut, was 6,373 square feet, the 
dimensions of the stones being 1.8 feet rise, 3.6 feet long, and 2.7 feet deep; 
and the average day’s work in cutting the beds to lay f-inch joints was 18.7 
square feet. The granite coping, composed of two courses—one of 12-inch 
rise, 30-inch bed, and 34-feet average length, and one of 24-inch rise, 48-inch 
bed, and 24-feet average length,—the top being pean-hammered, the face 
being rough with chisel draft around it, and the beds and joints cut to lay 
4-inch joints, required 6.1 days’-work of the cutter per cubic yard. 

“ In cutting the granite for the gate-houses of the Croton Reservoir at Eighty- 
sixth Street, New York City, in 1861-2, the minimum day’s work for a cutter 
was fixed at 15 superficial feet of joint. This included also the cutting of a 
chisel draft around the face of the stone, which costs per linear foot about one 
fourth as much as a square foot of joint, making the actual limit equivalent 
to about 17.7 square feet of joint. On this work, the proportion to be added 
to the cost of the cutters to give the total cost was as follows, the average for 
19 months’ work: for superintendence 8 per cent.; sheds and tools 7; sharpen¬ 
ing tools 11; labor moving stone in yard 10; drillers plugging off rough faces 
4; making a total of 40 per cent, to be added.” 

Note 4. Cost of Laying Cut Stone, f Most of the cut stone was laid by 
one mason, more than two not being employed at any time. The mason’s 
gang also shifted derricks. The cost of hauling stone to the work varied 
with the position of the blocks in the yard and whether they were assorted 
there into courses or lay promiscuously. The amount of labor required in 
laving the masonry was as follows: 

* From an account of the construction of the Boyd’s Corner dam on the Croton River 
Bear New York City, by J. James R. Croes, in Trans. Am. Soc. of C. E., Vol. III., pp. 3G3-64. 

4 Ibid., p. 365. 























546 


SUPPLEMENTARY NOTES. 


[APP. II* 


Labor Required in Laying Cut-stone Masonry. 



Amount per 

Cubic Yard. 

Kind of Labor. 

Hoisted by Hand. 

Hoisted by Steam. 


5 ft. 

10 to 20 ft. 

20 to 30 ft. 

30 to 50 ft. 

Mason, days. 

0.120 

0.119 

0.082 

0.108 

Laborers, days . 

0.184 

0.18S 

0.145 

0.155 

Mortar mixer, days. 

0.100 

0.82 

0.076 

0.101 

Derrick and carmen, days. 

0.327 

0.341 

0.235 

0.261 

Engine, hours. 

.... 

• • • 

0.462 

0.490 

Teams from yard, days.. 

0.100 

0.056 

0.056 

0.110 

Labor loading teams, days. 

0.184 

0.223 

0.223 

0.086 

Number of cubic yards laid. 

1,070 

2,2 

!70 

2,530 


Note o. Cost of Breaking Stone for Concrete.* “ The stone [gneiss] for 
the concrete was broken to be not more than 2 inches in its largest dimension. 
A Blake stone-breaker of 15 inch jaw. driven by a 15-borse-power engine, was 
used. The stone, which was obtained from the surface and from old fence 
walls in the vicinity of the work, was tough, and used up the jaws very fast. 
A movable jaw ordinarily lasted 20 days. The stone was delivered to the 
breaker by carts, having been lirst sledged to the proper size—about 12 inches 
square by 6 inches thick. The machine, when running at full speed, with 
one man feeding, two men supplying him with stone, one keeping the screen 
clear and helping to till barrows, two wheeling away the stone, and one on 
the dump, could break 144 cubic feet in an hour, or at tho rate of 54.4 cubic 
yards per day of 10 hours. This excessive speed was kept up, however, only 
as long as it was known that an inspector was timing it. The average rate 
of breaking for the, last year was 3.8 cubic yards per hour, which maybe 
assumed as the economical rate for the 15-inch machine. The largest machine 
(20-inch) will break 8 cubic yards per hour, if fed to that capacity; but 6 cubic 
yards per hour is more economical. The following table gives the cost in 
time of breaking the stone: 

O 


Labor Required in Breaking Stone for Concrete. 


Kind of Labor. 

Days per Cubic Yard. 

1867 

1868 

1869 

1870 

Furnishing: Laborers sledging! . 

0.269 

0 322 

0.224 

0.410 

Laborers loading carts!. 


0.051 

0.042 

0.087 

Carts hauling . . . 

0.049 

0.092 

0.066 

0.118 

Breaking: Engine and machine %. . 

0.045 

0.037 

0.027 

0.026 

Labor tending machine!. 

0.360 

0.238 

0.158 

0.174 

Total number of cubic yards broken. 

2,410 

4.170 

5,720 

3,650 

Average number of cubic yards broken per day... 

22.1 

27.3 

36.8 

38.0 


* From an account of the construction of the Boyd's Corner dam on the Croton River 
near New York City, by J. James R. Croes. in Trans. Am. Soc. of C. E.. Vol. III., pp. 356-58. 

t “ The difference in sledging is accounted for thus: In 1867 many fence-wall and cobble 
stones were used, which needed no sledging, but were hard to crush. In 1868 refuse from 
the quarry, which required sledging, was almost exclusively used. In 1869 stone-yard and 
quarry spalls were used. In 1870 the stone was quarried for the breaker; and consequently 
nearly all 'tf it was sledged. The carting and tending varied in the same way as above, for 
the same reasons.” 

$ Includes cost of engine driver and helpers, fuel and repairs of engine—about 0.05 of 
the wages of a day laborer per cubic yard. 














































APP. II.] 


SUPPLEMENTARY NOTES. 


547 


Note G. Cost of Imbedding Large Stones in Concrete.* * * § “The large un¬ 
wrought stone laid in the concrete, from the foundations to within 45 feet of 
the top of the dam, were set in full mortar beds and the surfaces plastered 
just before concrete was laid around them. The setting was done mostly by 
laborers, one mason superintending. The cost in day’s work per cubic yard 
was as follows : 


Labor Required to Imbed Large Stones in Concrete. 


• 

Kind of. Labor. 

Days per Cubic Yard. 

18671 

1868 % 

Foreman (mason). 

0.046 

0.057 

Laborers setting . 

0.208 

0.142 

“ plastering . 

0.085 

0.056 

“ mixing mortar.. 

0.078 

0.083 

“ at derrick . 

0.238 

0.254 

“ loading teams. 

.... 

0.305 

Teams transporting stone. 

0.160 

0.073 

Total quantity laid, cubic yards. 

1.234 

2.353 

Per cent, of whole mass. 

32.0 

36.6 


“ The cost of the mass of concrete and large stone, as laid in 1867, was 

per cent, of the cost of the concrete alone; and in 1868 it was 84^ per 
cent, of such cost. If the large stones do not exceed 25 percent, of the mass, 
the cost of the mass is reduced about 10 per cent, below concrete cost, while 
its specific gravity is increased about 8 per cent.” 

Note 7. Crushing Strength of Sewer Pipe. Experiments made at 
Chicago in 1879 by W. D. Hotchkiss, and reported to the author by Black- 
mer and Post, of St. Louis, gave the strength of ordinary sewer-pipe as fol¬ 
lows, when tested as described on page 408: one 12-inch and five 15-inch 
pipes failed at an average pressure of 8,504 lbs. per sq. ft. of horizontal sec¬ 
tion; and two 12-inch and two 15-inch were not crushed by an average pres¬ 
sure of 9,068 lbs. per sq. ft. 

Note 8. Holding Power of Drift Bolts. According to experiments 
made under the author’s direction,§ the average holding power of a 1-inch 
round rod driven into a ff-incli hole in pine, perpendicular to the grain, is 
501 pounds per linear inch (8 tons per linear foot); and under the same con¬ 
ditions the holding power of oak is 1,300 pounds per linear inch (7.8 tons per 
linear foot). The holding power of a bolt driven parallel to the grain is 
almost exactly half as much as when driven perpendicular to the grain. If 
the holding power of a 1-inch rod in a if-inch hole be designated as 1, the 
holding power in a jf-inch hole is 1.69, in a ff-incli hole 2.13, and in a ff-inch 
hole 1.09. The holding power decreases very rapidly as the bolt is withdrawn. 

Another series of experiments | using round and square drift-bolts in the 
same size holes shows that round drifl-bolts have the advantage over square 
ones, both in ultimate holding power and in holding power per pound of 
metal. 


* J. James R. Croes in Trans. Am. Soc. of C. E., Vol. III., p. 362. 

t Stone lowered an average of 20 feet. 

% One half lowered 5 feet; one quarter swung in level; one quarter hoisted 6 feet. 

§ Selected papers of the Civil Engineers’ Club of the University of Illinois, No. 4, prede¬ 
cessor of The Technograph, pp. 53-58. 

|| The Technograph , University of Illinois, No. 5, pp. 39-41. 






























INDEX 


ABU—ARC 

Abutments of arches, dimensions of exist¬ 
ing, 505 

stability, empirical formulas for, 499 
theory of, 492 

Abutments of bridges, contents, 357, 361, 363 
detailed plans, 356, 360, 362 
foundation, 364 
general form, 353 
Quality of masonry, 365, 385 
I -abutment, 362 
contents, 363 
detailed plan, 362 
U-abutment, 359 
contents, 361 
detailed plan, 360 
wing abutment, 355 
contents, 357 
detailed plan, 356 
Air-chamber, filling, 297 
Air-lock, for pneumatic pile, 281 
for pneumatic caisson, 284, 291, 299 
position, 290 

Arch, abutment of, stability, 492, 499 
backing, 505 
brick, 510 

center, camber. 523 
definitions, 515 

examples. Cabin John arch, 525 
stone bridges, 
tunnel arch, 512 
Washington bridge, 524 
load supported, 516 
outline forms. 519, 520, 522 
striking, method, 523 
time, 527 
culvert, 419 
cost, 434 
examples, 424 

Atchison, T. & S. F., segmental, 429 
cost, 438 

semi-circular, 429 
cost, 437 

Chicago, K. & N., semi-circular, 427 
cost, 436 

Illinois Central, semi-circular, 424 
cost, 435 

standard segmental, 429 
cost, 438 

junction of wings to body, 420 
masonry, cost of, 157, 159, 160 
quality of, 432 

specifications, foundations, 432, 533 
masonry. 432, 531 
paving, 148 

segmental vs. semi-circular, 421 
splay of wings, 419 
definition, of kinds of arches, 441 
of part ■> of an arch, 440 


ARC 

Arches, dimensions of abutments, 505 
of arches, 502 

rules derived from practice, 494 
thickness of abutment, 499 
thickness at crown, American pro© 
tice, 495 

English practice, 496 
French practice, 496 
thickness at springing, 498 
drainage 508 
elastic, theory of, 491 
engravings, 505 
inverted, for foundations, 212 
joint of rupture, 457 
line of resistance, definition, 443 
location. 453 

hypothesis of least preesure. 554 
hypothesis of least crown thrust, 455 
joint of rupture, 457 
Navier's principle, 465 
Winkler’s hypothesis, 463 
masonry, 432 
backing, 505 
cost, 157, 159, 160 
specifications, brick, 176, 177 
stone, 432, 515, 531 

relieving arches for retaining walls, 352 
in spandrel filling, 506 
spandrel, filling, q, v., 503 
stability, criteria of safety, 447 
conclusion, 452 
crushing, 448 
open joints, 451 
maximnm pressure, 451 
unit pressure, 449 
rotation, 448 
sliding, 452 
theories, 465 
elastic arch, 491 
external forces. 444 
method of employing, 466 
method of failure. 446 
rational theory, 466 
criterion, 473 
symmetrical load, 466 
general solution, 466 
special solution, 469 
unsymmetrical load, 471 
Scheffler’s theory, 474 
algebraic solution, 475 
erroneous solution, 480 
graphical solution, 479 
reliability, 481 
Rankines theory, 482 
curvature of linear arch, 482 
method of applying, 487 
reliability. 490 

various theories referred to, 491 

549 




550 


INDEX. 


ART—BRI 

Artificial stone, 112 
Beton-Coignet, 113 
Frear, 114 
McMurtrie, 113 
Portland, 113 
Ransome, 114 
Sorel, 115 
Ashlar, 138 
backing.140 
bond,139 
definitions, 136 
dressing, 138 

mortar required per yard, 141 
pointing, 141 
specifications, 142 
w here employed, 142 
Atchafalaya bridge, foundations, 273 
Atchison, Topeka & Santa Fe, bridge abut¬ 
ment, 359 

culvert, iron pipe, 414 
segmental arch, 429, 431.438 
semi-circular arch. 429, 430, 437 
Ax, and Tooth-ax, 126 

Batter, definition, 135 
Bearing piles, 219 
Bearing power, piles, q. v., 233 
soils, q. v., 188 
B6ton, see Concrete. 

B6ton-Coignet, 113 

Bismarck bridge, pressure on foundation, 
377 

Blair bridge, pier, 383 
pneumatic foundation, caisson, 284 
cost, 303 

frictional resistance, 297 
rate of sinking, 295 
Blasting in compressed air. 295 
Brick, absorptive power, 21, 39, 45 
arches, bond, 510 
examples, 511, 513, 514 
burning, 31 
classification, 35 
cost. 4? 

fire-brick, how made, 35 
elasticity, co-efficient of, 14 
masonry. 161 
bond, 163 
cost, 157, 160 

data for estimates, brick required, 173 
labor required, 174 
mortar required, 174 
impervious to water, 178 
joints, finishing, 162 
thickness, 161 
strength, 164 
compressive, 164 
pressure allowed, 167 
transverse, 167 

specifications, arches, 177 532, 542 
buildings, 175, 541 
sewers, 176 

vs. stone masonry, 177 
moulding, 34 
requisites for good, 37 
size, 46 

strength, crushing, 41 

condition of surface, 42 
data, 43-46 
form of specimen, 42 
size of specimen, 41 
transverse 40 
data. 13, 45 
weight, 46 

Bridge abutment, see Abutment. 


BRI—CEM 

Bridge masonry, cost, 157, 160 
Bridge piers, see Piers. 

Bond, brick arches, 510 
brick masonry, 163 
stone masonry, 139 
Box-culvert masonry, cost, 157, 160 
Brooklyn-bridge foundations, cost, 303 
description. 298 
pressure, 377 
Bush-hammer, 126 
Building-stones, classification, 24 
requisites for good, 3 
tests, 5 ; see also Stone. 

Buildings, data for computing weight of, 
200 

specifications for brick-work for, 541 

Cain’s profile for masonry dams, 329 
Cairo bridge, frictional resistance of caisson, 
297 

pier, outline of, 372 
pressure on foundation, 377 
stability of, 371 
stones in a course of. 385 
Caisson, definitions, 266 
disease, 300 
pneumatic. 284. 286 
Blair bridge. 284 
first use of, 280 
guiding, 295 

Havre de Grace bridge, 286 
Canadian box culvert, 406 
Cavil, 126 
Cement, 51 

amount required per yard of mortar, 83 
burning, thoroughness of, 56 
classification, 51 
cost, 54 

data for estimates, 86 . 88 
lime-cement mortar, 100 
mortar, see Mortar, 
natural. 52 
definition, 52 
specifications, 78.9 
tests, see tests below, 
weight, per barrel, 54 
Portland, constancy of volume, 78d 
cost, 54 
description, 52 

specifications, 78e. 78/, 7 89 . 787i 
strength, 67, 78a. 78d, 7Se, 78/, 78 h 
tests, see tests below, 
weight per barrel, 54 
Rosendale, definition, 53 
slag, 54 

specifications, quality, American, 78g 
English, 78e 
French, 78e 
German, 78d 

delivery and storage, 78h _ 

tests, 55 
activity, 57, 60 

burning, thoroughness of, 56 
chemical analysis, 63, 78e 
color, 55 

constancy of volume, 78d, 78e. 789 , 78/i 
fineness, 65, 66 , 78d, 78e, 78/, 78 9 , 78/i 
set, time of, 60 
soundness, 60, 78d, 78e, 78p 
accelerated, tests of, 63 
specific gravity, 56 
strength,67 
age when tested. 76 
data, 78a, 78d. 78e. 78/, 789 , 78h 
form of briquette, 72 







INDEX, 


551 


CEM—CUL 

Cement tests,strength, mixing the mortar, 71 
rapidity of applying the stress, 78 
water required, 68 
weight, 54, 56 
Centrifugal pump, 264 

Center of foundation, proper position of, 
202 


Center of gravity of trapezoid, to find, 318 
Center of pressure on foundation. 202 
Channeling and wedging, quarrying by, 123 
Chisel, pitching, 127 
splitting. 128 
tooth,128 

Chicago, K. & N. arch culvert, 427, 436 
Co efficient of friction, foundations, 276 


masonry, 315 
Coffer-dam, definition. 258 
construction, 258, 289 
double, 261 

Havre de Grace bridge, 289 
iron,261 
leakage, 262 
movable, 261 

process, for foundations, 214, 258 
Compressed air, physiological effect, 299 
Compressed-air process for foundations, 
see Foundations, pneumatic. 

Concrete, 106 
aggregate, 107 
cost, 112w, 157, 160, 265 
depositing under water, 112 o 
estimates, data for, 112/ 


economics of, 113a 
ingredients for a yard, 112 g, 1127i 
laying, 112n 
mixing. 112m 

proportions, theory of, 109 


strength, 112p 
compressive, 112p 
transverse, 112u 
water required, 112 j 
weight, 112u 

Concrete and piles for foundations, 254 
Connecticut brown-stone, 30 

1-v—136 

Cost, see the article in question. 
Coulomb’s theory of retaining wall, 341 
Cover stones for box culverts, 398 
theory for thickness, 398 
formulas, 399 
practical data, 401 
Cramps, 136 
Crandall, 127 
Crib for coffer-dam, 260 
Culvert, arch, see Arch, 
iron pipe, 412 
construction, 412 
cost, 416 

dimensions of the pipe, 412 
end walls, contents of, 414 
examples, 414, 415 
large, 416 

weight of the pipe, 412 
stone box, 396 
Canadian, 406 
contents, 403, 404, 405 
cost, 405 

cover stones, q. v., 398 
dimensions, 403, 404, 405 
double, 405 
end walls, 398 
examples, 403. 404, 406 
foundation, 397 
masonry, quality of, 401 
specifications, 401, 531 


CUL— EFF 

Culvert, stone box, Standard form, 402, 403 
West Shore R. R., 402, 404 
timber box, 417 
timber barrel, 418 
vitrified pipe, 407 
construction, 408 
cost of the pipe, 410 
end walls, 409 
examples, 411 
material required, 411 
strength of the pipe, 408 
water-way required, 391 
formulas, 393 
for quantity of flow, 394 
Meyer’s for the area, 394 
Talbot’s for the area, 394 
practical method of finding, 395 
Cushing pile foundation, 255 
Cylindrical surface, method of forming in 
stone, 129 

/ 

Dam, arched vs. gravity, 330 
bibliography, 334 
curved gravity, 331 
earth, 335 
gravity, 311 
masonry, 311 
arched,311 
Cain’s profile, 329 
classification, 311 

gravity, condition for stability of, 312 
crushing, 320 
maximum pressure, 322 
tension in masonry, 324 
limiting pressure, 325 
nomenclature, 312 
overturning. 317 
by moments, 317 
by resolution of forces, 320 
plan, 329 

arched vs. gravity, 330 
curved gravity, 331 
straight crest vs. straight toe, 329 
pressure allowable, 325 
profile, 326 
Cain’s, 329 
Krantz’s, 328 
method of finding, 327 
Quaker Bridge, 328 
sliding, 313 

quality of masonry, 333 
when employed, 335 
width on top, 326 
rock-fill, 334 
cost, 337 

when employed, 336 
stone-filled timber crib, 335 
Dimension stones, 136 
Disk piles, described, 218 
bearing power, 249 
Dorchester sandstone, 30 
Dowel, 136 
Dredges, 271 
Milroy, 272 

Morris & Cumming’s, 272 
mud pump, 292 
Dredging thro’ tubes, 271 
Drift bolts, described, 253 
holding power, 253 
Drills used in quarrying, 118 
Dynamite, 121 
driving piles with, 227 

Eads’ mud-pump, 292 
Efflorescence on brick-work, 181 




552 


IXDEX. 


ELA—FOU 

Elastic arch, theory of, 491 
Engravings, for list of, see Table of Con¬ 
tents. 

Estimates, data for, brick, 46, 47,173, 174 
< emeut, 86, 88 
lime, 86 
mortar, 88, 89 
sand, T9A;, 88 

Excavator, compressed-air, 272; see also 
Dredges and Pumps. 

Explosives, 119 
dynamite, 121 
gunpowder, 119 
nitro-glycerine, 120, 124 
quarrying by, 117 
Extrados defined, 440 

Face-hammer, 125 
Facing, defined, 135 
Feathers and Plug, described, 128 
Figures, for list of, see Table of Contents. 
Footings, off-set for masonry, 208 
steel rail, 212, 540 
timber, 211 

Forth bridge, pneumatic caisson*. 298 
Foundation, Atchafalaya bridge, 273 
bearing power of cla} r , 190 
bearing power of rock, 188 
bearing power of sand, 192 
bearing power of semi-liquid soil, 193 
summary, 194 
bed of, defined, 183 
bridge piers, 255, 257; see also below. 
buildings, 186 
area required, 201 

bearing power of soils, q. v. above, 188 

consolidating the soil, 197 

depth required, 195 

drainage, 195 

effect of wind, 204 

examination of site, 186 

footings, see Footings. 

grillage, q. v., 215, 254 

load to be supported, 199 

piles, see Piles. 

piles and grillage, 253 

piles and concrete, 254 

preparing the bed, 213 

sand piles, 197 

sand in layers, 198 

springs, 196 

coffer-dam process, 214, 258 
construction of the dam, 258 
thickness, 259 
puddle wall, 260 
leakage, 262 
pumps, q. v., 263 
preparing the bed, 264 
cost, 264 

compressed-air process, see pneumatic 
•process, below, 
concrete, 103, 215, 265 
cost of various processes compared, 310 
crib and erect caisson process, 266 
construction of the caisson, 267 
construction of the crib, 269 
excavating the site, 270 
principle of the method, 267 
definitions, 183 
drainage, 195 

dredging through wells, 271 
dredges, q. v., 271 
cost, 277 
iron tubes t 278 
timber cribs, 278 


FOU 

Foundation, examination of site, 186 
examples, 272 
Atchafalaya bridge, 273 
brick cylinders, 275 
Hawkesbury bridge, 275 
Poughkeepsie bridge, 272 
frictional resistance in sinking, 275 
iron, cast, 276 
wrought, 277 
masonry, 277 
freezing process, 307 
advantages, 309 
cost, 308 
details, 307 
history, 307 
principle, 307 

footings, see Footings above, 
frictional resistance, 275 
iron cylinders, 276 
masonry cylinders, 277 
pneumatic caissons, 297 
wood piles, 247, 248 
grillage, 215 

Hawkesbury bridge. 275 
independent, 204, 540 
inverted arch, 212 
lateral yielding, 255 
pile, see Piles, 
piles and grillage, 253 
piles and concrete, 254 
preparing the bed, 213, 264 
Point Pleasant bridge, cost, 265 
Poughkeepsie bridge, described, 272 
pneumatic piles, 281 
bearing power, 275, 283, 297 
cost, 304, 305 
pneumatic process, 278 
advantages, 306 
air-chamber, 284, 297, 298 
air-lock construction, 281, 284, 290, 299 
position, 290 
caisson, 284 
Blair bridge, 284 

Havre de Grace bridge, q. v., 286 
compressed-air process, 279 
cost, Blair, 303 
Brooklyn, 303 

European examples, 304, 310 
Havre de Grace, 302 
Plattsmouth, 304 
Philadelphia, 302, 304 
definitions, 278 
examples. Brooklyn, 298 
Forth, 298 

Havre de Grace, 286 
St. Louis, 297 
excavators, 291 
blasting, 295 
mud-pump. 292 
sand-lift, 291 
water-column, 294 
filling the air-chamber, 297 
frictional resistance, q. v., 275, 283, 297 
guiding the caisson, 295 
history, 219 

physiological effect of corhpressed-air, 
299 

plenum process, 279 
rate of sinking, 295 
vacuum process, 278 
sand in layers, 198 
sand-piles, 197 
steel-rail footings, 212 
timber in, 269 
timber footings, 211, 215 





INDEX. 


553 


FOU—LIM 

Foundation, under water, 257 
vacuum process, 278 
wind, effect of, 204 
Freezing of mortar, 100 
Freezing weather, specification for laying 
masonry in, 543 

Freezing process for foundations, q. v., 307 
Friction-clutch pile-driver, 223 
Friction, co-efficient of, for foundations, 
276 

for masonry, 315 

Frictional resistance in sinking foundations, 
q. v., 247, 248, 275, 297 
Frost batter, 364 

Grand Forks pivot pier, 380 
Grillage, 215 
Grout, 89 
Gunpowder, 119 
cost, 120 

efficiency in blasting, 120 
Gunpowder pile-driver, 226 

Hammer, bush, 126 
face. 125 
hand, 127 
patent, 127 

Haunch of an arch, defined, 440 
Havre de Grace bridge, pneumatic founda¬ 
tions of, 286 
air-lock, 291 
caisson, 286 
coffer-dam, 289 
cost, 302 
dimensions, 290 
frictional resistance, 297 
guiding the caisson, 295 
machinery, 290 
materials, quantity of, 290 
mud-pump, 292 
fate of sinking, 295 
Henderson bridge, top of pier, 384 
Hydraulic cement, see Cement. 

Hydraulic lime, 51, 82 

Ice, effect on stability of pier, 368 
Illinois Central arch culverts, 424, 435 
Impervious brick-work, 178 
Impervious mortar, 101 
Independent piers for foundations, 204 
Intrados, defined, 440 
Inverted arch for foundation, 212 
Iron coffer-dam, 261 

Iron cylinders for foundations, bearing pow¬ 
er of, 283 
cost, 302. 304 

frictional resistance in sinking, 276 
method of sinking, 274, 281 
Iron piles, 216 

Jet vs. hammer pile-driver, 229 
Joint of rupture, defined, 457 
method of finding, 457 
Petit’s theory, 462 

Xrantz’s profile for masonry dams, 328 

Laitance, 112p 
Lake Superior sandstone, 31 
Lateral yielding of foundations, 255 
Leakage of coffer-dams, 262 
Lime, cost, 50 
data for estimates, 86 
described, 49 
hydraulic, 51 


LIM—MOR 

Lime, preserving, 50 
testing, 50 

weight per barrel, 50 
Lime mortar, 81 
strength, 91 

Lime-cement mortar, 100 

Machines, pile-driving, 221 
Masonry, ashlar, see Ashlar, 
brick, see Brick, 
co-efficient of friction, 315 
cost, actual, arch culvert, 157, 160 
bridge pier, 157, 160 
railroad masonry, 157, 160 
stone, 155 
cutting, 156 
summary, 160 
tunnel masonry, 157 
U. S. public buildings, 
cutting the stone, 156 
masonry complete, 156 
cost, estimated, 153 
ashlar, 154 
dressing, 153 
quarrying, 153 
rubble, 155 
dressing, 153 
quarrying, 153 
definitions of kinds, 136 
footings, off-sets for, 208 
general rules for, 138 
measurement, brick, 172, 529 
stone, 151, 529, 539 
mortar required per|yard, 87 
off-sets for footings, 208 
pedestal, specifications for, 385 
specifications, see Specifications, 
squared-stone, see Squared-stone, 
stone, see Stone, 
strength of, 148 
brick, compressive, 164 
transverse, 167 
stone, allowed pressure, 149 
safe pressure, 150 
rubble, see Rubble, 
weight of, 200 

Measurement of masonry, brick, 172, 529 
stone, 151, 529, 539 
Medina sandstone, 31 
Mortar, absorptive power, 21 
amount required per yard of masonry, 89 
cement, change of volume in setting, 62, 
cement-lime. 100 [78<2, 78e, 78a 

co-efficient of elasticity of, 14 
compression of, 104 
cost, 95 

elasticity, 14, 104, 
estimates, data for, 86 
freezing, effect of, 102 
grout, 89 

hydraulic cement, 83 
hydraulic lime, 82 
ingredients for a yard, 88 
impervious to water, 101 
lime, 81 

lime-cement, 100 
natural vs. Portland, 92, 95 
Portland vs. natural, 92, 95 
proportioning, method of, 83 
re-tempering, 99 
strength, 87 
adhesive, 93 
compressive, 92 
increases with age, 91 
tensile, 90 





INDEX 




MOR—PIL 

Mortar, strength, transverse, 13 
water required, 68 
Mud-pump, 292 

Nipper pile-driver, 223 
Nitro-glyceriue, 120, 124 


Open joints in an arch, 451 


Patent hammer, 127 
Paving, 148, 532 
cost, 157, 160 

for foundations, 397, 432, 533 
Philadelphia, pneumatic piles, cost at, 302 
standard brick sewers. 513 
Physiological effect of compressed air, 299 
Piclc, 126 

Piers, contents, 387, 388 
cross section, 378 
examples, 372, 383, 381, 385 
Cushing’s pile, 255 
dimensions, bottom. 378 
examples. 372, 380, 383-86 
top, 377, 384 

foundations, 257; see also Foundations, 
iron tubular, 274, 387 
location, 366 

masonry, cost of, 157,160 
qualtiy of, 379 
specifications, 381, 537 
pivot, 379 
stability of, 367 
crushing, theory of, 371 
numerical example, 375 
current, effect of, 367 
foundation, pressure on, 376 
ice, effect of, 368 
overturning, theory of, 369, 370 
numerical example, 374 
resisting forces, 369 
sliding, theory of, 367 
numerical example, 371 
wind, effect of, 367 
timber-barrel, 388 
Piles, bearing power of, disk, 249 
screw, 249 
wood, actual, 247 
experiments on, 246 
factor of safety, 249 
formulas, empirical, 241 
author’s, 245 
Beaufoy’s, 243 
Engineering News’, 245 
Haswell’s, 242 
Mason’s 243 
Nystroms, 243 
Sander’s, 244 
Trautwine’s, 244 
rational. 234 
author's, 239 
Rankine’s, 241 
Weisbach’s, 241 

frictional resistance of, 247, 248 
load, safe, 248 
ultimate, 247 
butt vs. top down, 251 
t»aps. 220 
capping, 250 

concrete and piles, in foundations, 254 
cost, 230 

definitions of kinds, 216 
disk, described, 218 
bearing pow r er, 249 


PIL—PUM 

Pile foundations, 250 
concrete, 254 
cost, 310 
grillage, 253 
position of piles, 250 
sawing off the piles, 252 
iron, 216 

cylinders, 274, 281 
cost, 304 

sinking, frictional resistance, 273 
method of, 214, 281 
disk, q. v., 218 
screw, q. v., 217 

pneumatic, 281 ; see also Foundations, 
pneumatic, 
sand,197 
sawing off, 252 
screw, 217 
bearing pow r er, 249 
sheet, 219 
shoes, 220 

specifications, 220, 533 
splicing, 221 
top vs. butt down, 251 
used to consolidate soil, 197 
wood, 219 

bearing pow r er,see bearing power, above 
specifications, 220, 533 
Pile-driver, 221 
drop hammer, 222 
friction clutch, 223 
nipper, 223 

steam vs. drop hammer, 225 
dynamite, 227 
friction clutch, 223 
gunpow'der, 226 
hammer vs. jet, 229 
jet of water, 227 
nipper, 223 
steam, 224 

drop hammer vs. steam, 225 
water-jet, 227 
hammer vs. jet, 229 
Pile-driving, cost of, 230 
bridge construction, 231 
foundations, 232 
harbor work, 233 
railroad construction, 230 
railroad repairs, 231 
river protection, 233 
Pitching chisel, 127 
Pivot pier, 379 

Plane surfaces, method of forming in stone, 
129 


Plates, for list of, see Table of Contents. 
Plattsmouth bridge, cost of concrete founda¬ 
tions at, 265 

cost of pneumatic foundations, 304 
pressure on foundations, 377 
rate of sinking by pneumatic process, 295 
Plug and feathers, 128 
Pneumatic foundations, see Foundations, 
pneuma'ic. 

Point. 127 

Pointing, 141 [ 0(55 

Point Pleasant bridge, cost of foundation, 
Poughkeepsie bridge, foundation described 
272 

Pozzuolana. 53 

Pressure allowed on masonry, brick, 166, 167 
stone. 149, 151 
Puddle, 260 
Pulsometer, 264 
Pumps, 263 
hand, 263 






INDEX. 


555 


PUM—SEW 

Pumpo, centrifugal, 2o4 
for’waier-jet pile-driver, 228 
mud-pump, 292 
pufcometer, 264 
steam siphon, 263 

Quarrying, 116 

by channeling and wedging, 123 
by explosives, 117 
by hand tools, 116 
Quoin, defined, 136 

Railroad masonry, classification, is 2 
cost, 157, 160 
specifications, 529, 534 
Rankine’s theory of the arch, 482 
Relieving arches for retaining walls, 352 
Resistance, frictional, in sinking founda¬ 
tions, 247, 248, 275, 297 
Retaining walls. Coulomb’s theory, 341 
definitions, 338 
difficulties in theories, 339 
dimensions, empirical rules for, 

Benj. Baker’s, 349 
English, 349 
Ttautwine’s, 349 
drajnage, 350 
failure, method of, 338 
land-ties, 351 
Rankine’s theory, 348 
stability, theory of. 339, 340 
applicability of, 348 
assumptions necessary, 340 
Coulomb’s theory, 341 
surcharged wall, 343 
reliability, 343 
Rankine’s theory, 348 
Weyrauch’s theory, 343 
general formula, 344 
horizontal earth-surface, 345 
surcharge, 345 
reliability, 346 

Weyrauch’s theory, q. v., 343 
Riprap, 148, 532 
cost, 157, 160 
Rubble masonry, 145 
cost, 157, 160 
coursed, 137 

mortar required per yard, 89, 146 
specifications, 147, 531, 536, 541 
uncoursed, 137 

Sand, amount per yard of mortar, 88 
cost, 79 k 

data for estimates, 86 
foundations, used for. 197, 198 
requisites for good, 796 
cleanness, 79c 
durability, 796 
fineness, 79 d, 79i 
sharpness, 796 
voids, 79 g, 79 i 
weight, 79 i, 79 k 
Sand-lift, 291 
Sand-pump, 292 

Sandstones, those most frequently used, 31 
Scheffier’s theory of arch, 474 
Schuylkill bridge,cost of pneumatic piles,302 
Screw-piles, described, 217 
bearing power, 249 
Seasoning of stone, 18 
Sewers, brick arches for, 

Philadelphia standard, 513 
Washington standard, 514 


SEW—STE 

Sewer-pipe, cost. 410 
strength. 408, 547 
weight, 410 

Sibley bridge, guiding the caisson, 296 
piers, specifications for, 381 
Skew arch, defined, 442 
Slope-wall masonry, 147 
cost, 157, 160 
specifications, 147, 531 
Soap and alum wash for brick-work, 178 
Soffit, defined, 440 
Soil, bearing power of, 188 
clay, 190 
rock,188 
sand, 192 

semi-liquid soil, 193 
summary, 194 
testing, method of, 187 
examining, method of, 186 
improving, method of, 195 
Spandrel, defined, 440 
filling, arches in, 508 
drainage of, 508 
Specifications, 

arch culvert masonry, 432, 531 
architectural masonry, 534, 539 
ashlar, 142, 530 
box culverts, 401, 531 
brick-work, arches, 177, 532 
buildings, 175, 541 
sewers, 176 
bridge piers, 381 
cement, 78d, 78e, 78/, 78 g, 7Sh 
concrete, 532, 535, 540 
foundations, 432, 533 
masonry, 
arch culvert,'432 
ashlar, 142 
brick-work, 175, 177 
buildings, architectural, 539 
railroad, 534 
paving, 148 
pedestal, 385 
pier, 381, 

rubble. 147,.531, 536, 541 
slope-wall, 147 
squared-stone, 144 
paving, 148 
piers, 381, 539 
piles, 220, 533 

rubble masonry, 147, 531, 536, 541 
slope-wall masonry, 147, 531 
squared-stone masonry, 144, 530, 538 
Splicing piles, 221 
Squared-stone masonry, 143 
definitions, 137 
pitched-face, 137 
quarry-face, 137 
range work, 137 
mortar required per yard, 144 
specifications, 144, 530, 538 
Standard arch culvert, 249 
contents, 433 

cost, 438 , 

dimensions, 433 

Standard stone-box culvert, 402 
contents, 403 
cost, 405 
dimensions, 403 
St. Genevieve sandstone, 31 
St. Louis bridge foundations, 297 
maximum pressure on, 377 
Steam pile-driver, 224 
drop-hammer vs. steam, 225 
Steam siphon, 263 







556 


INDEX. 


STE—STO 

Steel-rail footings, 212, 540 
Stone, absorbing power, 21 
Stone, argillaceous, 26 
artificial, 1136 
calcareous, 26 
cost, 155 

crushing strength, 8 
cushions, 9 
data, 11 

fracture, form of, 9 
specimen, dressing, 10 
form, 8 
size, 8 
slabs, 11 
cut-stone, 132 
axed,133 

brush-hammered, 134 
crandalled, 133 
diamond panel, 134 
fine-pointed, 133 
rough-pointed, 132 
rubbed,134 
tooth-axed, 133 
description, artificial, 112 
granite, 27 
limestone, 28 
marble, 28 
sandstone, 29 
trap, 27 

durability, 4, 15 
destructive agents, 16 
preserving, methods of, 23 
resisting agents, 17 
seasoning, effect of, 18 
testing, method of, 20 
artificial, 20 
absorptive power, 21 
acid, effect of, 23 
atmosphere, effect of, 23 
Brard’s method, 23 
crushing strength, 8 
frost, effect of, 21 
microscopical examination, 23 
natural, 20 
elasticity, 14 
ranite, 27 
ardness, 7 
limestone, 28 
local names, 32 
marble, 28 
market price, 155 
masonry, q. v., definitions, 135 
measurement of, 151, 529, 539 
requisites for good, 3 
sandstones, description of principal, 29 
siliceous, 26 
specific gravity, 6 
squared, drafted, 132 


STO—YAZ 

Stone, squared, pitch-faced, 132 
quarry-faced, 132 
strength, crushing, q. v., 6 
transverse, 13 
tests, bibliography of, 15 
toughness, 7 
vs. brick masonry, 177 
weight, 7 

Stone-cutting tools, described, 125 
Stone grinder, 129 
Stone planer, 129 
Stone polisher, 129 
Stone saws, 128 

Surfaces, method of forming, 129 
method of finishing, 131 

Timber, barrel culvert, 419 
box culvert, 417 
footing, 211 
foundations, 269 
Tremie, 107 

Vitrified pipe, cost, 410 
strength, 408, 547 
weight, 410 

Wall, definitions of parts of a, 135 
Warped surface, method of forming, 131 
Washington brick sewers, 514 
Water required for cement mortar, 68 
concrete, 112 j 
Water-jet pile-driver. 227 
vs. hammer pile-driver, 229 
Water-way for culverts, 391 
factors, 391 
formulas, 393 
Meyer’s, 394 
Talbot’s, 394 
Waverly sandstone, 31 
Weep holes, 351 

West Shore stone-box culvert, 402, 404 
Weyrauch’s theory of retaining walls, 343 
“White-wash” on brick-work, 181 
Wind, effect on foundation, 204 
pressure, amount of, 201 
Wood bearing-piles, see Piles. 

Weight, brick, 46 
buildings, 200 
cast-iron pipe, 412 
cement, barrel, 54 
cubic foot, 56 
lime, 50 
masonry, 200 
sand, 79 k 
stone, 7 

vitrified-pipe, 410 

Yazoo River bridge, guiding the caisson, 296 





PLATE I. 

CAISSON, CRIB AND COFFER-DAM. 

Havre de Grace Bridge. 

FOR TEXT, SEE PAGE 28& 













Plate 


I. PNEUMATIC 

FOR TEXT. SEE PAGE 286. 


CAISSON, 


CRIB, and COFFER-DAM. 

SCALE OF FEET ■ — — — — - 



^ z' rods 























































































































































































































































































































































































































f 



PLAN 



































































































































































PLATE II. 


6-FOOT ARCH CULVERT. 

Illinois Central Standard. 

FOR TEXT, SEE PAGE 424. 
























































































































































PLATE III. 


8-FOOT ARCH 

C. K. AND N. 
FOR TEXT, SEE 


CULVERT. 

Standard. 

PAGE 427. 






K/3^> 
























































































































































































































PLATE IV. 


10-FOOT ARCH CULVERT, 

SEMI-CIRCULAR. 

A. T. and S. F. Standard. 

FOR TEXT, SEE PAGE 429 






* 


V 

/ 

/ 




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N. 

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TRANSVERSE SECTION. 



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LO2STG-ITLJI0IXT.A.XJ SECTION 


PLATE V 

10-Foot Segmental Arch Culvert. 


A.. T. & S. F. STANDARD 


FOR TEXT SEE PACE 42ft 









































































































































































PLATE V. 

10-FOOT ARCH CULVERT. 

SEGMENTAL. 

A. T. and S. F . Standard, 

FOR TEXT, SEE PAGE 429. 


> 








</ 3 ‘ 



















































































































































PLATE VI, 


12-FOOT STANDARD ARCH CULVERT. 


FOR TEXT, SEE PAGE 429. 























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3 00 

12 50 
2 00 
7 00 
7 50 

2 50 
2 00 
1 25 

15 00 

10 00 
5 00 

3 00 
1 50 


2 



























* Ingalls’s Ballistic Tables.8vo, $1 50 

Handbook of Problems in Direct Fire.8vo, 4 00 

Mahan’s Permanent Fortifications. (Mercur.).8vo, half morocco, 7 50 

*Mercur’s Attack of Fortified Places.12mo, 2 00 

“ Elements of the Art of War.8vo, 4 00 

Metcalfe’s Ordnance and Gunnery.12mo, with Atlas, 5 00 

Murray’s A Manual for Courts-Martial.16mo, morocco, 1 50 

Infantry Drill Regulations adapted to the Springfield 

Rifle, Caliber .45.32mo, paper, 10 

* Phelps’s Practical Marine Surveying.8vo, 2 50 

Powell’s Army Officer’s Examiner.12mo, 4 00 

Sharpe’s Subsisting Armies.32mo, morocco, 1 50 

Very’s Navies of the World.8vo, half morocco, 3 50 

Wheeler’s Siege Operations.8vo, 2 00 

Winthrop’s Abridgment of Military Law.12mo, 2 50 

Woodhull’s Notes on Military Hygiene.16mo, 1 50 

Young’s Simple Elements of Navigation..lGmo, morocco, 2 00 

“ “ “ “ “ first edition. 1 00 


ASSAYING. 

Smelting—Ore Dressing—Alloys, Etc. 

Fletcher’s Quant. Assaying with the Blowpipe.. 16mo, morocco, 1 50 

Furman’s Practical Assaying.8vo, 3 00 

Kunhardt’s Ore Dressing.8vo, 1 50 

O’Driscoll’s Treatment of Gold Ores.8vo, 2 00 

Ricketts and Miller’s Notes on Assaying.8vo, 3 00 

Thurston’s Alloys, Brasses, and Bronzes.8vo, 2 50 

Wilson’s Cyanide Processes.12mo, 1 50 

“ The Chlorination Process.12mo, 1 50 


ASTRONOMY. 

Practical, Theoretical, and Descriptive. 

Craig’s Azimuth .4to, 3 50 

Doolittle’s Practical Astronomy.8vo, 4 00 

Gore’s Elements of Geodesy.8vo, 2 50 

Hayford’s Text-book of Geodetic Astronomy.8vo. 3 00 

* Michie and Harlow’s Practical Astronomy.8vo, 3 00 

* White’s Theoretical and Descriptive Astronomy.12mo, 2 00 































BOTANY. 

Gardening for Ladies, Etc. 


Baldwin’s Orchids of New England.Small 8vo, $1 50 

Loudon’s Gardening for Ladies. (Downing.).12mo, 1 50 

Thome’s Structural Botany.16mo, 2 25 

Westermaier’s General Botany. (Schneider.).8vo, 2 00 


BRIDGES, ROOFS, Etc. 

Cantilever—Draw—Highway—Suspension. 
{See also Engineering, p. 8.) 


Boiler’s Highway Bridges.8vo, 2 00 

* “ The Thames River Bridge.4to, paper, 5 00 

Burr’s Stresses in Bridges.8vo, 3 50 

Crehore’s Mechanics of the Girder.8vo, 5 00 

Dredge’s Thames Bridges.7 parts, per part, 1 25 

Du Bois’s Stresses in Framed Structures.Small 4to, 10 00 

Foster’s Wooden Trestle Bridges.4to, 5 00 

Greene’s Arches in Wood, etc.8vo, 2 50 

“ Bridge Trusses.8vo, 2 50 

“ Roof Trusses.8vo, 1 25 

Howe’s Treatise on Arches.8vo, 4 00 

Johnson’s Modern Framed Structures.Small 4to, 10 00 

Merriman & Jacoby’s Text-book of Roofs and Bridges. 

Part I., Stresses.. ,8vo, 2 50 

Merriman & Jacoby’s Text-book of Roofs and Bridges. 

Part II.. Graphic Statics.8vo, 2 50 

Merriman & Jacoby’s Text-book of Roofs and Bridges. 

Part III., Bridge Design.Svo, 2 50 

Merriman & Jacoby’s Text-book of Roofs and Bridges. 

Part IV., Continuous, Draw, Cantilever, Suspension, and 

Arched Bridges.8vo, 2 50 

*Morison’s The Memphis Bridge.Oblong 4to, 10 00 

Waddell’s Iron Highway Bridges...Svo, 4 00 

“ De Pontibus (a Pocket-book for Bridge Engineers). 

16mo, morocco, 3 00 

Wood’s Construction of Bridges and Roofs.Svo, 2 00 

Wright’s Designing of Draw Spans. Parts I. and II..Svo, each 2 50 

“ “ “ “ “ Complete.8vo, 3 50 


4 


























CHEMISTRY—BIOLOGY—PHARMACY. 

Qualitative—Quantitative—Organic—Inorganic, Etc. 

Adriance’s Laboratory Calculations.12mo, 

Allen’s Tables for Iron Analysis.Svo, 

Austen’s Notes for Chemical Students.12mo, 

Bolton’s Student’s Guide in Quantitative Analysis.8vo, 

Boltwood’s Elementary Electro Chemistry. (In the press .) 

Classen’s Analysis by Electrolysis. (Herrick and Bolt\vood.).8vo, 

Cohn’s Indicators and Test-papers.12mo 

Crafts’s Qualitative Analysis. (Schaeffer.).12mo, 

Davenport’s Statistical Methods with Special Reference to Bio¬ 
logical Variations.12mo, morocco, 

Drechsel’s Chemical Reactions. (Merrill.).12mo, 

Fresenius’s Quantitative Chemical Analysis. (Allen.).8vo, 

“ Qualitative “ “ (Johnson.).8vo, 

“ “ “ “ (Wells.) Trans. 

16th German Edition.Svo, 

Fuertes’s Water and Public Health.12mo, 

Gill’s Gas and Fuel Analysis.12mo, 

Hammarsten’s Physiological Chemistry. (Maudel.).8vo, 

Helm’s Principles of Mathematical Chemistry. (Morgan). 12mo, 

Kolbe’s Inorganic Chemistry.12mo, 

Ladd’s Quantitative Chemical Analysis.12mo, 

Landauer’s Spectrum Analysis. (Tingle.).8vo, 

Lob’s Electrolysis and Electrosynthesis of Organic Compounds. 

(Lorenz.). 12mo, 

Mandel’s Bio-chemical Laboratory.12mo, 

Mason’s Water-supply. 8vo, 

“ Examination of Water.12mo, 

Meyer’s Radicles in Carbon Compounds. (Tingle.) (In the press .) 

Miller’s Chemical Physics.8vo, 

Mixter’s Elementary Text-book of Chemistry.12mo, 

Morgan’s The Theory of Solutions and its Results.12mo, 

“ Elements of Physical Chemistry.12mo, 

Nichols’s Water-supply (Chemical and Sanitary).8vo, 

O’Brine’s Laboratory Guide to Chemical Analysis.8vo, 

Perkins’s Qualitative Analysis.12mo, 

Pinner’s Organic Chemistry. (Austen.).12mo, 


$1 25 
3 00 
1 50 

1 50 

3 00 

2 00 
1 50 

1 25 
1 25 
6 00 

3 00 

5 00 
1 50 
1 25 

4 00 
1 50 
1 50 
1 00 
3 00 

1 00 
1 50 


5 00 


1 25 

/ 

2 00 

1 50 
1 00 

2 00 
2 50 
2 00 
t 00 
1 50 
































Poole’s Calorific Power of Fuels.8vo, 

Ricketts and Russell’s Notes on Inorganic Chemistry (Non- 

metallic). Oblong 8vo, morocco, 

Ruddiman’s Incompatibilities in Prescriptions.8vo, 

Sckimpf’s Volumetric Analysis.12mo, 

Spencer’s Sugar Manufacturer’s Handbook.16mo, morocco, 

“ Handbook for Chemists of Beet Sugar Houses. 

16mo, morocco, 

Stockbridge’s Rocks and Soils.8vo, 

* Tillman’s Descriptive General Chemistry.8vo, 

Van Deventer’s Physical Chemistry for Beginners. (Boltwood.) 

12mo, 

Wells’s Inorganic Qualitative Analysis.12mo, 

“ Laboratory Guide in Qualitative Chemical Analysis. 

8vo, 

Whipple’s Microscopy of Drinking-water.8vo, 

Wieclimann’s Chemical Lecture Notes.12mo, 

“ Sugar Analysis.Small 8vo, 

Wulling’s Inorganic Phar. and Med. Chemistry.12mo, 


$3 00 


75 

2 00 

2 50 
2 00 

3 00 

2 50 

3 00 


1 50 
1 50 

1 50 
3 50 
3 00 

2 50 
2 00 


DRAWING. 

Elementary—Geometrical—Mechanical—Topographical. 


Hill’s Shades and Shadows and Perspective.8vo, 2 00 

MacCord’s Descriptive Geometry.8vo, 3 00 

“ Kinematics.8vo, 5 00 

“ Mechanical Drawing.8vo, 4 00 

Mahan’s Industrial Drawing. (Thompson.).2 vols., 8vo, 3 50 

Reed’s Topographical Drawing. (II. A.). .4to, 5 00 

Reid’s A Course in Mechanical Drawing.8vo. 2 00 

“ Mechanical Drawing and Elementary Machine Design. 

8vo. (In the press.) 

Smith’s Topographical Drawing. (Macmillan.).8vo, 2 50 

Warren’s Descriptive Geometry.2 vols., 8vo, 3 50 

Drafting Instruments.12mo, 1 25 

“ Free-hand Drawing.12mo, 1 00 

“ Linear Perspective.12mo, 1 00 

“ Machine Construction.2 vols., 8vo, 7 50 


6 



























Warren’s Plane Problems 


.12mo, 

“ Primary Geometry.:.12mo, 

“ Problems and Theorems.8vo, 

“ Projection Drawing...12mo, 

Warren’s Shades and Shadows.8vo, 

“ Stereotomy—Stone-cutting...8vo, 

Wlielpley’s Letter Engraving.12mo, 

ELECTRICITY AND MAGNETISM. 

Illumination—Batteries—Physics—Railways. 

Anthony and Brackett’s Text-book of Physics. (Magie.) Small 

8vo, 

Anthony’s Theory of Electrical Measurements.12mo, 

Barker’s Deep-sea Soundings.Svo, 

Benjamin’s Voltaic Cell.8vo, 

“ History of Electricity.8vo, 

Classen’s Analysis by Electrolysis. (Herrick and Boltwood.) 8vo, 

Cosmic Law of Thermal Repulsion.12mo, 

Crehore and Squier’s Experiments with a New Polarizing Photo- 

Chronograph.8vo, 

Dawson’s Electric Railways and Tramways. Small, 4to, half 

morocco, 

* Dredge’s Electric Illuminations.. . .2 vols., 4to, half morocco, 

“ “ “ Vol. II.4to, 

Gilbert’s De magnete. (Mottelay.).8vo, 

Holman’s Precision of Measurements.8vo, 

“ Telescope-mirror-scale Method.Large 8vo, 

Lob’s Electrolysis and Electrosynthesis of Organic Compounds. 

(Lorenz.).. • • *12mo, 

*Michie’s Wave Motion Relating to Sound and Light.Svo, 

Morgan’s The Theory of Solutions and its Results.12mo, 

Niaudet’s Electric Batteries. (Fishback.).12mo, 

Pratt and Alden’s Street-railway Road-beds.8vo, 

Reagan’s Steam and Electric Locomotives.12mo, 

Thurston’s Stationary Steam Engines for Electric Lighting Pur- 

.8vo, 

.8vo, 


25 


75 


2 50 

1 50 

3 00 

2 50 
2 00 ' 


3 00 
1 00 
2 00 
3 00 
3 00 
3 00 
75 

3 .00 

12 50 
25 00 
7 50 
2 50 
2 00 
75 

1 00 

4 00 
1 00 
2 50 
2 00 
2 00 


poses.... 
*Tillman’s Heat 


7 


2 50 
1 50 



























ENGINEERING. 


Civil—Mechanical—Sanitary, Etc. 

(See also Bridges, p. 4; Hydraulics, p. 9; Materials of En¬ 
gineering, p. 10; Mechanics and Machinery, p. 12 ; Steam 
Engines and Boilers, p. 14.) 


Baker’s Masonry Construction.8vo, 

“ Surveying Instruments...12mo, 

Black’s U. S. Public Works.Oblong 4to, 

Brooks’s Street-railway Location...16mo, morocco, 

Butts’s Civil Engineers’ Field Book.16mo, morocco, 

Byrne’s Highway Construction.8vo, 

“ Inspection of Materials and Workmanship.16mo, 

Carpenter’s Experimental Engineering .8vo, 

Church’s Mechanics of Engineering—Solids and Fluids_8vo, 

“ Notes and Examples in Mechanics.8vo, 

Crandall’s Earthwork Tables. 8vo, 

The Transition Curve.16mo, morocco, 

* Dredge’s Penn. Railroad Construction, etc. Large 4to, 

half morocco, 

* Drinker’s Tunnelling.4to, half morocco, 

Eissler’s Explosives—Nitroglycerine and Dynamite.8vo, 

Folwell’s Sewerage.8vo, 

Fowler’s Coffer-dam Process for Piers.8vo. 

Gerhard’s Sanitary House Inspection.12mo, 

Godwin’s Railroad Engineer’s Field-book.lGmo, morocco, 

Gore’s Elements of Geodesy.Svo, 

Howard’s Transition Curve Field-book.16mo, morocco, 

Howe's Retaining Walls (New Edition.). . .. .12mo, 

Hudson’s Excavation Tables. Yol. II. Svo, 

Hutton’s Mechanical Engineering of Power Plants.Svo, 

“ Heat and Heat Eugines.Svo, 

Johnson’s Materials of Construction.Large Svo, 

“ Stadia Reduction Diagram. .Sheet, 22£ X 28£ inches, 

“ Theory and Practice of Surveying.Small Svo, 

Kent’s Mechanical Engineer’s Pocket-book.lGmo, morocco, 

Kiersted’s Sewage Disposal.12mo, 

Mahan’s Civil Engineering. (Wood.).Svo, 

Merriman and Brook's Handbook for Surveyors.. . .lGmo, mor., 

Merriman’s Precise Surveying and Geodesy.Svo, 

“ Retaining Walls and Masonry Dams.Svo, 

“ Sanitary Engineering.Svo, 

Nagle’s Manual for Railroad Engineers.lGmo, morocco, 

Ogden’s Sewer Design.12mo, 

Patton’s Civil Engineering.Svo, half morocco, 


$5 00 
3 00 
5 00 

1 50 

2 50 

5 00 

3 00 

6 00 
6 00 
2 00 
1 50 

1 50 

20 00 
25 00 

4 00 

3 00 

2 50 
1 00 
2 50 
2 50 
1 50 
1 25 
1 00 

5 00 

5 00 

6 00 
50 

4 00 

5 00 

1 25 
5 00 

2 00 

2 50 
2 00 
2 00 

3 00 
2 00 
7 50 


8 




































Patton’s Foundations.Svo, 

Pratt and Alden’s Street-railway Road-beds.Svo, 

Rockwell’s Roads and Pavements in France.12mo, 

Searles’s Field Engineering ... .=.16mo, morocco, 

“ Railroad Spiral.lGmo, morocco. 

Siebert and Biggin’s Modern Stone Cutting and Masonry.. .8vo, 

Smart’s Engineering Laboratory Practice.12mo, 

Smith’s Wire Manufacture and Uses.Small 4to, 

Spalding’s Roads and Pavements...12mo, 

“ Hydraulic Cement.12mo, 

Taylor’s Prismoidal Formulas and Earthwork.8vo, 

Thurston’s Materials of Construction .8vo, 

* Trautwine’s Civil Engineer’s Pocket-book-16mo, morocco, 

* “ Cross-section.Sheet, 

* “ Excavations and Embankments.Svo, 

* “ Laying Out Curves.12mo, morocco, 


Waddell’s De Pontibus (A Pocket-book for Bridge Engineers). 

16mo, morocco, 

Wait’s Engineering and Architectural Jurisprudence.Svo, 

Sheep, 


“ Law of Field Operation in Engineering, etc.Svo. 

Warren’s Stereotomy—Stone-cutting.8vo, 

Webb’s Engineering Instruments. New Edition. 16mo, morocco, 

Wegmann’s Construction of Masonry Dams. 4to > 

Wellington’s Location of Railways.. -.Small Svo, 

Wheeler’s Civil Engineering.Svo, 

Wolff’s Windmill as a Prime Mover.8vo, 


$5 00 
2 00 
1 25 
3 00 
1 50 

1 50 

2 50 

3 00 
2 00 
2 00 

1 50 
5 00 

5 00 
25 

2 00 

2 50 

3 00 

6 00 
6 50 

2 50 
1 25 
5 00 
5 00 

4 00 

3 00 


HYDRAULICS. 

Water-wheels—Windmills—Service Pipe—Drainage, Etc. 

{See also Engineering, p. 8.) 

Bazin’s Experiments upon the Contraction of the Liquid Vein. 

(Train wine.).^ v0> 

Bovey’s Treatise on Hydraulics.Svo, 4 00 

Coffin’s Graphical Solution of Hydraulic Problems.12mo, 

Ferrel’s Treatise on the Winds, Cyclones, and Tornadoes.. .8vo, 4 00 

Fuertes’s Water and Public Health.•.12mo, 1 50 

Gane-uillet & Kutter’s Flow of Water. (Hering & Trautwine.) 

8vo, 4 00 

Hazen’s Filtration of Public Water Supply.Svo, 

Herschel’s 115 Experiments..^Svo, 2 00 

Kiersted’s Sewage Disposal.12mo, 1 25 


9 






























Mason’s Water Suppl}’ - .8vo, $5 00 

“ Examination of Water.12mo, 1 25 

Merriman’s Treatise on Hydraulics...8vo, 4 00 

Nichols’s Water Supply (Chemical and Sanitary).8vo, 2 50 

Wegmann’s Water Supply of the City of New York.4to, 10 00 

Weisbach’s Hydraulics. (Du Bois.).8vo, 5 00 

Whipple’s Microscopy of Drinking Water.8vo, 8 50 

Wilson’s Irrigation Engineering.8vo, 4 00 

“ Hydraulic and Placer Mining.12mo, 2 00 

Wolff’s Windmill as a Prime Mover.8vo, 3 00 

Wood’s Theory of Turbines.8vo, 2 50 

MANUFACTURE 5. 

Boilers—Explosives—Iron—Steel—Sugar—Woollens, Etc. 

Allen’s Tables for Iron Analysis.8vo, 3 00 

Beaumont’s Woollen and Worsted Manufacture.12mo, 1 50 

Bollaud’s Encyclopaedia of Founding Terms.12mo, 3 00 

“ The Iron Founder.12ino, 2 50 

“ “ “ “ Supplement.12mo, 2 50 

Bouvier’s Handbook on Oil Painting.12mo, 2 00 

Eissler’s Explosives, Nitroglycerine and Dynamite.8vo, 4 00 

Ford’s Boiler Making for Boiler Makers.18mo, 1 00 

Metcalfe’s Cost of Manufactures.8vo, 5 00 

Metcalf’s Steel—A Manual for Steel Users.12mo, 2 00 

* Reisig’s Guide to Piece Dyeing.8vo, 25 00 

Spencer’s Sugar Manufacturer’s Handbook .. . .16mo, morocco, 2 00 
“ Handbook for Chemists of Beet Sugar Houses. 

16mo, morocco, 3 00 

Thurston’s Manual of Steam Boilers. 8vo, 5 00 

Walke’s Lectures on Explosives.8vo, 4 00 

West’s American Foundry Practice...12mo, 2 50 

Moulder's Text-book .12mo, 2 50 

Wiechmann’s Sugar Analysis.. Small 8vo, 2 50 

Woodbury’s Fire Protection of Mills. 8vo, 2 50 

MATERIALS OF ENGINEERING. 

Strength—Elasticity—Resistance, Etc. 

(See also Engineering, p. 8.) 

Baker’s Masonry Construction.8vo, 5 00 

Beardslee and Kent’s Strength of Wrought Iron.8vo, 1 50 

Bovey’s Strength of Materials.8vo, 7 50 

Burr’s Elasticity and Resistance of Materials.8vo, 5 00 

Byrne’s Highway Construction.8vo, 5 00 


10 



































Church’s Mechanics of Engineering—Solids and Fluids.Bvo, $G 00 

Du Bois’s Stresses in Framed Structures.Small 4to, 10 00 

Johnson’s Materials of Construction.8vo, G 00 

Lanza’s Applied Mechanics.Bvo, 7 50 

Martens’s Testing Materials. (Henning.).2 vols., Bvo, 7 50 

Merrill’s Stones for Building and Decoration.Bvo, 5 00 

Merriman’s Mechanics of Materials.Bvo, 4 00 

“ Strength of Materials.12mo, 1 00 

Patton’s Treatise on Foundations.Bvo, 5 00 

Rockwell’s Roads and Pavements in France.12mo, 1 25 

Spalding’s Roads and Pavements.12mo, 2 00 

Thurston’s Materials of Construction...Bvo, 5 00 

“ Materials of Engineering.3 vols., 8vo, 8 00 

Yol. I., Nou-metallie .Bvo, 2 00 

Yol. II., Iroh and Steel.Bvo, 8 50 

Yol. III., Alloys, Brasses, and Bronzes. .8vo, 2 50 

Wood’s Resistance of Materials.Bvo, 2 00 

MATHEMATICS. 

Calculus—Geometiiy—Trigonometry, Etc. 

Baker’s Elliptic Functions.Bvo, 1 50 

Ballard’s Pyramid Problem.Bvo, 1 50 

Barnard’s Pyramid Problem.Bvo, 

*Bass’s Differential Calculus.12mo, 4 00 

Briggs’s Plane Analytical Geometry.12mo, 1 00 

Chapman's Theory of Equations.12mo, 1 50 

Compton’s Logarithmic Computations.12mo, 1 oO 

Davis’s Introduction to the Logic of Algebra.8vo, 1 50 

Halsted’s Elements of Geometry....Bvo, 1 7o 

“ Synthetic Geometry.Bvo, 

Johnson’s Curve Tracing.. • • .12mo, 1 00 

“ Differential Equations—Ordinary and Partial. 

Small 8vo, 3 50 

“ Integral Calculus.12mo, 1 50 

“ “ “ Unabridged. Small 8vo. 

{In the press.) 

“ Least Squares.12mo, 1 50 

*Ludlow’s Logarithmic and Other Tables. (Bass.).Bvo, 2 00 

* “ Trigonometry with Tables. (Bass.).Bvo, 3 00 

*Mahan’s Descriptive Geometry (Stone Cutting).8vo, 1 50 

Merriman and Woodward’s Higher Mathematics.8vo, 5 00 

Merriman’s Method of Least Squares.Bvo, 

Parker's Quadrature of the Circle .... .-. 8v0 - 2 50 

Rice and Johnson’s Differential and Integral Calculus, 

2 vols. in 1, small 8vo, 2 50 


11 






































Rice and Johnson’s Differential Calculus.Small 8vo, $3 00 

“ Abridgment of Differential Calculus. 

Small 8vo, 1 50 

Totten’s Metrology.8vo, 2 50 

Warren’s Descriptive Geometry.2 vols., 8vo, 3 50 

“ Drafting Instruments.12mo, 1 25 

“ Free-hand Drawing.12mo, 1 00 

“ Linear Perspective.12mo, 1 00 

“ Primary Geometry.12mo, 75 

Plane Problems.12mo, 1 25 

Problems and Theorems.8vo, 2 50 

Projection Drawing.12mo, 1 50 

Wood’s Co-ordinate Geometry.8vo, 2 00 

“ Trigonometry.12ino, 1 00 

Woolf’s Descriptive Geometry.». Large 8vo, 3 00 

MECHANICS-MACHINERY. 

Text-books and Practical Works. 

{See also Engineering, p. 8.) 

Baldwin’s Steam Heating for Buildings.12mo, 2 50 

Barr’s Kinematics of Machinery.8vo, 

Benjamin’s Wrinkles and Recipes.12mo, 2 00 

Chordal’s Letters to Mechanics. 12mo, 2 00 

Church’s Mechanics of Engineering.8vo, 0 00 

Notes and Examples in Mechanics.8vo, 2 00 

Crehore’s Mechanics of the Girder.8vo, 5 00 

Cromwell’s Belts and Pulleys. 12mo, 1 50 

“ Toothed Gearing.12mo, 1 50 

Compton’s First Lessons in Metal Working.12mo, 1 50 

Compton and De Groodt’s Speed Lathe.12mo, 1 50 

Dana’s Elementary Mechanics.12mo, 1 50 

Dingey’s Machinery Pattern Making.12mo, 2 00 

Dredge’s Trans. Exhibits Building, World Exposition. 

Large 4to, half morocco, 10 00 

Du Bois’s Mechanics. Yol. I., Kinematics.8vo, 3 50 

“ “ Yol. II., Statics..•.8vo, 4 00 

“ “ Yol. III., Kinetics.8vo, 3 50 

Fitzgerald’s Boston Machinist.18mo, 1 00 

Flather’s Dynamometers.12mo, 2 00 

“ Rope Driving.12mo, 2 00 

Hall’s Car Lubrication.12mo, 1 00 

Holly’s Saw Filing.18mo, 75 

Johnson’s Theoretical Mechanics. An Elementary Treatise. 

{In the press.) 

Jones’s Machine Design. Part I., Kinematics.8vo, 1 50 

12 





































Jones’s Machine Design. Part II., Strength and Proportion oi' 

Machine Parts. 8vo, $3 00 

Lanza’s Applied Mechanics.8vo, 7 50 

MacCord’s Kinematics.8vo, 5 00 

Merriman’s Mechanics of Materials.8vo, 4 00 

Metcalfe’s Cost of Manufactures.8vo, 5 00 

*Michie’s Analytical Mechanics.8vo, 4 00 

Richards’s Compressed Air.12mo, 1 50 

Robinson’s Principles of Mechanism. 8vo, 3 00 

Smith’s Press-working of Metals.8vo, 8 00 

Thurston’s Friction and Lost Work..8vo, 3 00 

“ The Animal as a Machine.12mo, 1 00 

Warren’s Machine Construction.2 vols., 8vo, 7 50 

Weisbacli’s Hydraulics and Hydraulic Motors. (Du Bois.)..8vo, 5 00 
“ Mechanics of Engineering. Vol. III., Part I., 

Sec. I. (Klein.).....8vo, 5 00 

Weisbach’s Mechanics of Engineering. Yol. III., Part I., 

Sec. II. (Klein.).8vo, 5 00 

Weisbach’s Steam Engines. (Du Bois.).8vo, 5 00 

Wood’s Analytical Mechanics.8vo, 3 00 

“ Elementary Mechanics. 12mo, 1 25 

“ “ “ Supplement and Key.12mo. 1 25 

METALLURGY. 

Ikon—Gold—Silver—Alloys, Etc. 

Allen’s Tables for Iron Analysis.8vo, 3 00 

Egleston’s Gold and Mercury.Large 8vo, 7 50 

“ Metallurgy of Silver.Large 8vo, 7 50 

* Kerl’s Metallurgy—Copper and Iron.8vo, 15 00 

* “ “ Steel, Fuel, etc. 8vo, 15 00 

Kunhardt’s Ore Dressing in Europe. 8vo, 1 50 

Metcalf’s Steel—A Manual for Steel Users.12mo, 2 00 

O’Driscoll’s Treatment of Gold Ores.8vo, 2 00 

Thurston’s Iron and Steel.8vo, 3 50 

“ Alloys. ; .8vo, 250 

Wilson’s Cyanide Processes.12mo, 1 50 

MINERALOGY AND MINING. 

Mine Accidents—Ventilation—Ore Dressing, Etc. 

Barringer’s Minerals of Commercial Value.. ..Oblong morocco, 2 50 

Beard’s Ventilation of Mines.12mo, 2 50 

Boyd’s Resources of South Western Virginia.8vo, 3 00 


Brush and Peufield’s Determinative Mineralogy. New Ed. 8vo, 4 00 

13 


































■Chester’s Catalogue of Minerals. .8vo, $1 25 

“ “ “ “ .Paper, 50 

“ Dictionary of the Names of Minerals.8vo, 3 00 

Dana’s American Localities of Minerals.Large 8vo, 1 00 

“ Descriptive Mineralogy (E.S.) Large 8vo. half morocco, 12 50 
“ First Appendix to System of Mineralogy. .. Large 8vo, 1 00 

“ Mineralogy and Petrography. (J. D.).12mo, 2 00 

Minerals and How to Study Them. (E. S.)..12mo, 1 50 

“ Text-book of Mineralogy. (E. S.).. .New Edition. 8vo, 4 00 

* Drinker’s Tunnelling, Explosives, Compounds, and Rock Drills. 

4to, half morocco, 25 00 

Egleston’s Catalogue of Minerals and Synonyms.8vo, 2 50 

Eissler’s Explosives—Nitroglycerine and Dynamite.8vo, 4 00 

Hussak’s Rock-forming Minerals. (Smith.).Small Svo, 2 00 

Ihlseng’s Manual of Mining.Svo, 4 00 

Kunhardt’s Ore Dressing in Europe. Svo, 1 50 

O’Driscoll’s Treatment of Gold Ores.Svo, 2 00 

* Penfield’s Record of Mineral Tests.Paper, 8vo, 50 

Roseubusch’s Microscopical Physiography of Minerals and 

Rocks. (Hidings.).8vo, 5 00 

Sawyer’s Accidents in Mines.Large Svo, 7 00 

Stockbridge’s Rocks and Soils.Svo, 2 50 

Walke’s Lectures on Explosives.Svo, 4 00 

Williams’s Lithology.8vo, 3 00 

Wilson’s Mine Ventilation.12mo, 1 25 

“ Hydraulic and Placer Mining.12mo, 2 50 

STEAM AND ELECTRICAL ENGINES, BOILERS, Etc. 

Stationary—Marine—Locomotive—Gas Engines, Etc. 

(See also Engineering, p. 8.) 

Baldwin’s Steam Heating for Buildings.12mo, 2 50 

Clerk’s Gas Engine.*.Small Svo, 4 00 

Ford’s Boiler Making for Boiler Makers.ISmo, 1 00 

Hemenway’s Indicator Practice.12mo, 2 00 

Hoadley’s Warm-blast Furnace....*.. .8vo, 1 50 

Ivneass’s Practice and Theory of the Injector.8vo, 1 50 

MacCord’s Slide Valve.8vo, 2 00 

Meyer’s Modern Locomotive Construction.4to, 10 00 

Peabody and Miller’s Steam-boilers.8vo, 4 00 

Peabody’s Tables of Saturated Steam.8vo, 1 00 

“ Thermodynamics of the Steam Engine. 8vo, 5 00 

“ Valve Gears for the Steam Engine.Svo, 2 50 

Pray’s Twenty Years with the Indicator.Large Svo, 2 50 

Pupin and Osterberg’s Thermodynamics.12mo, 1 25 

14 



































Reagan’s Steam and Electric Locomotives.12mo, $2 00 

Rontgen’s Thermodynamics. (Du Bois.).8vo, 5 00 

Sinclair’s Locomotive Running.12mo, 2 00 

Snow’s Steam-boiler Practice.8vo. (In the press.) 

Thurston’s Boiler Explosions.12mo, 1 50 

“ Engine and Boiler Trials.8vo, 5 00 

“ Manual of the Steam Engine. Part I., Structure 

and Theory.. . ...8vo, 6 00 

“ Manual of the Steam Engine. Part II., Design, 

Construction, and Operation.8vo, 6 00 

2 parts, 10 00 

Thurston’s Philosophy of the Steam Engine.12mo, 75 

“ Reflection on the Motive Power of Heat. (Carnot.) 

12mo, 1 50 

“ Stationary Steam Engines.8vo, 2 50 

“ Steam-boiler Construction and Operation.8vo, 5 00 

Spangler’s Valve Gears.8vo, 2 50 

Weisbach’s Steam Engine. (Du Bois.).8vo, 5 00 

Whitham’s Constructive Steam Engineering.8vo, 6 00 

“ Steam-engine Design.8vo, 5 00 

Wilson's Steam Boilers. (Flather.).12mo, 2 50 

Wood’s Thermodynamics, Heat Motors, etc.8vo, 4 00 


TABLES, WEIGHTS, AND MEASURES. 

For Actuaries, Chemists, Engineers, Mechanics—Metric 


Tables, Etc. 

Adriance’s Laboratory Calculations.12mo, 1 25 

Allen’s Tables for Iron Analysis.8vo, 3 00 

Bixby’s Graphical Computing Tables..Sheet, 25 

Compton's Logarithms.12mo, 1 50 

Crandall’s Railway and Earthwork Tables.8vo, 1 50 

Egleston’s Weights and Measures.18mo, 75 

Fisher’s Table of Cubic Yards.Cardboard, 

Hudson’s Excavation Tables. Vol. II.8vo, 100 

Johnson’s Stadia and Earthwork Tables. 8vo, 1 25 

Ludlow’s Logarithmic and Other Tables. (Bass.).12mo, 2 00 

Totten’s Metrology.^vo, 3 

VENTILATION. 


Steam Heating—House Inspection—Mine Ventilation. 


Baldwin’s Steam Heating. 

Beard’s Ventilation of Mines. . 

Carpenter’s Heating and Ventilating of Buildings 

Gerhard’s Sanitary House Inspection. 

Reid’s Ventilation of American Dwellings.. 

Wilson’s Mine Ventilation. 


12mo, 
12mo, 
. .8vo, 
12mo, 
12mo, 
12mo, 


2 50 

2 50 

3 00 
1 00 
1 50 
1 25 


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MISCELLANEOUS PUBLICATIONS. 


Alcott’s Gems, Sentiment, Language.Gilt edges, $5 00 

Bailey’s The New Tale of a Tub.8vo, 75- 

Ballard’s Solution of the Pyramid Problem.8vo, 1 50 

Barnard’s The Metrological System of the Great Pyramid. .8vo, 1 50 

Davis’s Elements of Law.8vo, 2 00 

Emmon’s Geological Guide-book of the Rocky Mountains. .8vo, 1 50 

Ferrel’s Treatise on the Winds.8vo, 4 00 

Haines’s Addresses Delivered before the Am. Ry. Assn...12mo. 2 50 

Mott’s The Fallacy of the Present Theory of Sound. .Sq. IGnio, 1 00 

Ricketts’s History of Rensselaer Polytechnic Institute.... 8vo, 3 00 

Rotherham’s The New Testament Critically Emphasized. 

12mo, 1 50 

“ The Emphasized New Test. A new translation. 

Large 8vo, 2 00 


Totten’s An Important Question in Metrology.8vo, 2 50 

Whitehouse’s Lake Moeris.Paper, 25 

* Wiley’s Yosemite, Alaska, and Yellowstone.4to, 3 00 


HEBREW AND CHALDEE TEXT=BOOKS. 

For Schools and Theological Seminaries. 

Gesenius’s Hebrew and Chaldee Lexicon to Old Testament. 

(Tregelles.).Small 4to, half morocco, 5 00‘ 

Green’s Elementary Hebrew Grammar.12mo, 1 25 

“ Grammar of the Hebrew Language (New Edition).8vo, 3 00 

“ Hebrew Chrestomathy.8vo, 2 00 

Letteris’s Hebrew Bible (Massoretic Notes in English). 

8vo, arabesque, 2 25 

MEDICAL. 

Bull’s Maternal Management in Health and Disease.12mo, 1 00 

Hammarsten’s Physiological Chemistry. (Mandel.).8vo, 4 00 

Mott’s Composition, Digestibility, and Nutritive Value of Food. 

Large mounted chart, 1 25 

Ruddiman’s Incompatibilities in Prescriptions.8vo, 2 00 

Steel’s Treatise on the Diseases of the Ox.8vo, 6 00 

“ Treatise on the Diseases of the Dog.8vo, 3 50 

Woodhull’s Military Hygiene. 16mo, 1 50 

Worcester’s Small Hospitals—Establishment and Maintenance, 
including Atkinson’s Suggestions for Hospital Archi¬ 
tecture.12mo, 1 25 


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